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156 Cards in this Set
- Front
- Back
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What are isomers?
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Chemical compounds that have the same molecular formula but differ in structure.
Can be very similar or very different. |
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What are structural isomers?
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Compounds that share only their molecular formula.
Because their atomic connections maybe different, they often have very different chemical and physical properties. Also constitutional isomers. |
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What are stereoisomers?
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Compounds that have the same atomic connections, but the atoms are arranged differently in space.
Geometric isomers, enantiomers, diastereomers, meso compounds, and conformational isomers all fall under this heading. |
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What is meant by the term chiral?
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An object that is not superimposable upon its mirror image is called chiral.
Right and left hands are chiral. |
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A carbon must have how many substituents to be a chiral center?
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4
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What is an enantiomer?
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Chiral objects that are nonsuperimposable mirror images are called enantiomers and are a specific type of stereoisomer.
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All single bonds are what type of bond?
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Sigma bonds
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Shorter single bonds are stronger/weaker than longer bonds?
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Stronger
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What is a pi bond?
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When two p orbitals overlap in a parallel fashion.
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When both a sigma bond and a pi bond exist between two atoms, a __________ is formed.
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Double bond
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When a sigma bond and two pi bonds exists between two atoms, a ___________ is formed.
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Triple bond
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Pi bonds are weaker/stronger than sigma bonds?
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Weaker
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Carbon prefers what type of geometry?
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Tetrahedral
This geometry minimizes repulsion. |
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What type of hybridization does carbon most often take?
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sp3
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Give the component bond, hybridization, and angles of a single bond.
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Sigma bond
sp3 109.5 degrees |
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Give the component bond, hybridization, and angles of a double bond.
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Sigma, pi
sp2 120 degrees |
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Give the component bond, hybridization, and angles of a triple bond.
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sigma, pi, pi
sp 180 degrees |
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What is a primary carbon atom?
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A carbon atom bonded to only one other carbon atom.
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Describe some physical properties of alkanes.
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As molecular weight increases, melting pt, boiling pt, density also increase.
Branched molecules have slightly lower boiling and melting pts. Greater branching reduces surface area, so molecules are held less tightly, lowering boiling pt. |
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What are nucleophiles?
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Electron-rich species that are attracted to positively polarized atoms.
"nucleus lovers" |
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The best leaving groups are what and why?
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Weak bases.
Weak bases can accept and electron pair and dissociate to form a stable species. |
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What is the rate limiting, or rate determining step?
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The rate at which a reaction occurs can never be greater than the rate of its slowest step.
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What is the rate-limiting step of an Sn1 reaction?
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The dissociation of the molecule to form a carbocation.
Because this step is energetically unfavorable. |
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What is an Sn2 reaction?
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A reaction that involves a nucleophile pushing its way into a compound while simultaneously displacing the leaving group.
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What determines the rate of an Sn2 reaction?
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The concentrations of both the molecule w/ a leaving group and the nucleophile.
Because the rate of an Sn2 reaction depends on the concentration of two reactants, it follows 2nd order kinetics. |
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Sn1 reactions are favored in what type of solvent?
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Polar protic solvents
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The order of stability for carbocations in Sn1 reactions
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3 prime > 2 prime > 1 prime > methyl
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Which is more reactive: alkenes are alkanes?
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Alkenes
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Describe some physical properties of alkenes.
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Similar to those of alkanes.
Melting and boiling pts increase w/ increasing molecular weight. Terminal alkenes, or 1-alkenes, usually boil at lower temperature than internal alkenes. Trans-alkenes generally have higher melting pts than cis-alkenes, but lower boiling points because they are less polar. |
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Compare the physical properties of trans-alkenes with cis-alkenes.
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Trans-alkenes generally have higher melting pts than cis-alkenes because their higher symmetry allows better packing in the solid state.
Trans-alkenes tend to have lower boiling pts because they are less polar. |
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What is polarity?
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A property that results from the asymmetrical distribution of electrons in a particular molecule.
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What is the most common method for synthesizing alkanes?
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Elimination reactions
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Describe a unimolecular elimination (E1) reaction.
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E1 reaction is a 2 step process proceeding through a carbocation intermediate.
The elimination of a leaving group first followed by the removal a proton by a strong base in weak soln results in a double bond. E1 is favored by same factors that favor Sn1 reactions (Polar solvents, such as water, ethyl alcohol, or acetic acid) Dehydrohalogenation (-HX) and Dehydration (-H2O) are the main types of elimination rxns |
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Describe a bimolecular elimination (E2) reaction.
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A strong base removes a proton, while a halide ion anti to the proton leaves, resulting in a double bond.
Occurs in one step. The more substitued double bond is preferentially formed. |
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Describe a catalytic hydrogenation reaction.
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A reductive process of adding hydrogen to a double bond w/ the aid of a metal catalyst (platinum, palladium, nickel).
Results in cleavage of a double bond |
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Describe electrophilic addition reactions.
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Many different addition reactions exist, but most operate via the same essential mechanism.
Electrons of a pi bond are exposed and easily attacked by molecules that want to accept an electron pair (Lewis acids). Electron seeking = electrophiles |
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What is Markovnikov's rule?
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The proton will add to the less substituted carbon atom (the carbon atom w/ the most protons).
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Describe the addition of halogens (X2) to a double bond.
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Double bond acts as a nucleophile and attacks the X2 molecule, displacing X-.
Intermediate carbocation is a cyclic halonium ion. This is then attacked by X-, giving the dihalo compound. This addition is anti. |
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If the addition of halogens (X2) is carried out in a nucleophilic solvent, what can results other than the dihalo compound?
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A halo alcohol.
The solvent molecules compete in the displacement step producing the halo alcohol. The most common nucleophilic solvents are water and alcohol |
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Describe the addition of water to alkenes.
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Can occur under acidic conditions.
Double bond is protonated according the Markovnikov's rule, forming the most stable carbocation. This carbocation reacts w/ water, forming a protonated alcohol, which loses a proton to yield the alcohol. Performed at low temperatures b/c the reverse is an acid-catalyzed dehydration favored at high temperatures. |
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Describe free radical addition reactions.
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Disobey markovnikov's rule b/c X adds first instead of H+.
An alternate mechanism for the addition of HX to alkenes and occurs when peroxides, oxygen, or other impurities are present. Useful for HBr but not for HCl or HI. |
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Describe hydroboration
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Produces an alcohol w/ overall anti-Markovnikov, syn orientation.
Boron atom is a Lewis acid and attaches tot he less sterically hindered carbon atom. Second step is an oxidation-hydrolysis w/ peroxide and aqueous base. THF often used w/ BH3 intially. |
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Describe the oxidation of alkenes.
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Alkenes can be oxidized w/ KMnO4 (potassium permangenate).
Cold, dilute, aqueous KMnO4 produces 1,2 diols (vicinal diols) which are also called glycols. Hot, basic soln of KMnO4 nonterminal alkenes are cleaved forming molar equivalents of carboxylic acid. Terminal alkenes are cleaved to form a carboxylic acid and carbon dioxide. |
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Describe ozonolysis of alkenes.
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Treatment of alkenes w/ ozone (O3, often w/ CH2Cl2), followed by reduction w/ zinc and water results in cleavage of the double bond.
If also reduced w/ NaBH4 (sodium borohydride), alcohols are produced. |
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Describe polymerization reactions.
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Polymerization is the creation of long, high molecular weight chains (polymers).
Requires high temperature and pressures. |
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Ethyne is also called what?
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Acetylene
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Describe the physical properties of alkynes.
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Similar to those of alkenes and alkanes.
Shorter chain compounds are gases. Internal alkynes boil at higher temperatures than terminal alkynes. |
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How can alkynes be synthesized?
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Triple bonds can be made by the elimination of 2 molecules of HX from a geminal or vicinal dihalide.
Can also add an existing triple bond to a particular carbon skeleton. |
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In general, what is an aromatic compound?
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Aromatic compounds are cyclic, conjugated polyenes that possess 4n+2 pi electrons and adopt planar conformations to allow maximum overlap of the conjugated pi orbitals.
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What is Huckel's rule?
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The criterion of 4n+2 pi electrons to indicate aromaticity.
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What is an antiaromatic compound?
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A cyclic, conjugated polyene that possesses 4n electrons.
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What does ortho-, meta-, and para- mean?
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1,2 disubstituted compound = ortho- (o)
1, 3 = meta- (m) 1,4 = para- (p) |
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Describe electrophilic aromatic substitution.
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The most important reaction of aromatic compounds.
An electrophile replaces a proton on an aromatic ring. Most common are halogenation, sulfonation, nitration, and acylation. |
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List some activating, ortho/para directing substituents (electron donating).
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NH2, NR2, OH, NHCOR, OR, OCOR, and R.
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List some deactivating, ortho/para directing substituents (weakly electron withdrawing)
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F, Cl, Br, and I
Halogens are ortho/para directors, since they possess an unshared pair of electrons just as nitrogen does. However, the stability this provides is offset by the fact that halogens are substantially more electronegative than carbon, and thus draw electron density away from the pi system. This destabilizes the cationic intermediate, and EAS occurs less readily. Halogens are therefore deactivating groups. |
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List some deactivating, meta directing substituents (electron withdrawing).
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NO2, SO3H
Carbonyl compounds including COOH, COOR, COR, and CHO. |
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What are phenols?
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Compounds with the general formula ArOH (Ar=Aromatic Ring).
A hydroxyl group attached to an aromatic ring. |
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Why is the boiling point of alcohols significantly higher than analogous hydrocarbons?
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The higher boiling point is due to hydrogen bonding.
Molecules with more than one hydroxyl group show greater degrees of hydrogen bonding. |
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Hydrogen bonds typically form between what atoms?
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Hydrogen bonds form on the "FON" - Fluorine, Oxygen, Nitrogen.
Hydrogen bonding can occur when hydrogen atoms are attached to highly electronegative atoms, such as nitrogen and fluorine. HF had strong hydrogen bonds because the high electronegativity of fluorine causes the HF bond to be highly polarized. |
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Describe Ka and pKa in terms of acidity.
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Strong acids have high Ka's and small pKa's.
pKa = -log Ka |
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Compare the acidity of phenols with alipathic alcohols
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Phenols are much more acidic than alipathic alcohols
The hydroxyl hydrogens of phenols are more acidic due to resonance structures that distribute the negative charge throughout the ring, stabilizing the anion. Phenols can form salts w/ inorganic bases, such as NaOH. |
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Does acidity increase/decrease w/ the addition of more alkyl groups and why?
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Acidity DECREASES as more alkyl groups are attached b/c the electron-donating alkyl groups DESTABILIZE the alkoxide anion.
Therefore, electron-withdrawing groups STABILIZE the alkoxy anion, making the alcohol MORE acidic. |
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Regarding aromatic compounds, describe the effect of electron-withdrawing groups and electron-donating groups on acidity.
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Electron-withdrawing substituents increase acidity.
Electron-donating substituents decrease acidity. |
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Primary (1) alcohols oxidize to _________ which oxidizes to _________?
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(1) alcohol ----> aldehydes -----> carboxylic acids.
Primary alcohols oxidize to aldehydes which oxidizes to carboxylic acids. |
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Secondary (2) alcohols oxidize to ______?
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Ketones
(2) alcohols ----> ketones |
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Give the two most frequently used reducing reagents used in alcohol synthesis.
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LiAlH4 - Lithium aluminum hydride.
NaBH4 - Sodium borohydride. |
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Alcohols can be dehydrated to produce ________.
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Alkenes
Dehydration of alcohols is usually performed in a strong acidic solution (usually H2SO4). Mechanism is E1. |
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Is the hydroxyl group a good leaving group?
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No. Hydroxyl groups are poor leaving groups.
So the displacement of hydroxyl groups in substitution reactions is rare. |
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Describe phenols and electrophilic aromatic substitution.
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Phenols readily undergo electrophilic aromatic substitution, because it has lone pairs it can donate to the ring.
The -OH groups is a strongly activating, ortho/para directing ring substituent. |
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When you see a transition metal, such as Cr or Mn, with lots of oxygen (Cr2O7, CrO3, MnO4) think what?
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OXIDATION!
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Describe the oxidation of alcohols.
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The oxidation of alcohols generally invovles some form of chromium (VI) as the oxidizing agent, which is reduced to chromium (III) during the reaction.
Ex. PCC, KMnO4, NaCr2O7, CrO3) |
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What is PCC?
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Pyridinium chlorochromate (C5H6NCrO3Cl)
Used as a mild oxidizing reagent in the oxidation of alcohols. Converts primary alcohols to aldehydes without overoxidation of the acid. |
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Compare PCC and KMnO4.
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PCC is a mild oxidizing reagent which will convert primary alcohols to aldehydes.
KMnO4 is a very strong oxidizing reagent that will convert the alcohol all the way to a carboxylic acid. Also forms ketones from secondary alcohols. |
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What is Jones reagent?
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CrO3 (chromium trioxide) dissolved with dilute H2SO4 (sulfuric acid) in acetone.
This mixture oxidizes primary alcohols to carboxylic acids. Oxidizes secondary alcohols to ketones. |
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What is an ether?
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A compound w/ 2 alkyl (or aryl) groups bonded to an oxygen atom.
ROR |
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Nomenclature of ethers.
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Ethers (R-O-R) are named according to IUPAC rules as alkoxyalkanes, w/ the smaller chain as the prefix and larger chain as the suffix.
There is also a system in which ethers are named as alkyl alkyl ethers, and the alkyl substituents are alphabetized (methoxyethane would be ethyl methyl ether) EXCEPTIONS TO THESE RULES ARE CYCLIC ETHERS. |
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Describe the relation of ring size, angle strain, and stability.
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Smaller rings have MORE angle strain, making the LESS stable.
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Are ethers soluble in water?
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Ethers are only slightly polar and, therefore, only slightly soluble in water.
Ethers are rather inert to most organic reagents and are frequently used as solvents. |
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Describe the boiling point of ethers.
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Ethers boil at relatively low temperatures compared to alcohols. They boil close to the same temp. as alkanes of comparable molecular weight.
This is because ETHERS DO NOT UNDERGO HYDROGEN BONDING because they have no hydrogen atoms bonded to the oxygen atoms. |
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How are ethers synthesized?
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Williamson ether synthesis produces ethers from the rxn of metal alkoxides (CH3CH3CH3C-ONa) w/ primary alkyl halides (CH3-Br) or tosylates.
The alkoxides behave as nucleophiles and displace the halide or tosylate via Sn2 rxn producing an ether. The mechanism will not work upon secondary or tertiary alkyl halides because of competition from the E2 mechanism, which would form an alkene. |
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Ethers react with the oxygen in the air to form what?
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Peroxides (ROOR)
Peroxides are highly explosive compounds. |
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Describe the oxidation of tertiary alcohols.
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Tertiary alcohols can't be oxidized due to valence reasons.
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Carbonyl group
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C=O
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Aldehyde nomenclature
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In the IUPAC system, aldehydes are named w/ the suffix -al.
The position of the aldehyde group does not need to be specified: It must occupy the terminal (C-1) position. |
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Ketone nomenclature
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Ketones are named w/ the suffix -one.
The location of the carbonyl group must be specified w/ a number, except in cyclic ketones, where it is assumed to occupy the 1 position. |
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Describe the boiling point of aldehydes and ketones.
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The dipole moments associated with the polar carbonyl groups align, causing an elevation in boiling point relative to alkanes.
Elevation is less than alcohols, as no hydrogen bonding is involved. |
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What is Lindlar's catalyst?
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Palladium (Pd) on barium sulfate (BaSO4) w/ quinoline.
Used in reduction rxns. Quinoline stops the rxn at the alkene stage when used w/ alkynes. Product alkene is cis conformation. |
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Describe the Friedel-Crafts acylation reaction.
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In the Friedel-Crafts acylation rxn, a carbocation electrophile, usually an acyl group (an alkyl group attached to a carbon-oxygen double bond), is incorporated into the aromatic ring.
These rxns are usually catalyzed by lewis acids, such as AlCl3. |
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Many of the reactions of aldehydes and ketones share what general reaction mechanism?
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Nucleophilic addition to a carbonyl.
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Describe aldehyde and ketone addition reactions?
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General mechanism is the nucleophilic addition to a carbonyl.
The C=O bond is polarized w/ partial pos. on C and partial neg. on O. This makes the carbon a good target for nuclephilic attack. Nucleophile attacks, forming a bond with the carbon, causing the pi bond in the C=O bond to break. This generates a tetrahedral intermediate. If no good leaving group is present, the double bond can't reform, and the final product is nearly identical to the intermediated, except the oxygen will usually accept a proton to become a hydroxyl group. |
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Describe the hydration of aldehydes and ketones.
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In the presence of water, aldehydes and ketones react to form gem diols (1,1 diols).
WHEN WATER IS THE NUCLEOPHILE, HYDRATION OCCURS. |
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Describe acetal and ketal formation.
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This rxn is similar to hydration and occurs when aldehydes and ketones are treated w/ alcohols.
When one equivalent of alcohol is added to an aldehyde or ketone, the product is a hemiacetal or hemiketal respectively. When two equivalents of alcohol are added, the product is an acetal or a ketal respectively. Mechanism is same for hydration. WHEN R-OH IS THE NUCLEOPHILE, HEMIACETALS OR HEMIKETALS AND ACETALS OR KETALS ARE FORMED. |
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Describe the reaction of aldehydes and ketones with HCN (hydrogen cyanide).
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Aldehydes and ketones react w/ HCN to produce cyanohydrins.
HCN dissociates and the nucleophilic cyanide anion attacks the carbonyl carbon atom. Protonation of the oxygen produces the cyanohydrin. The cyanohydrin gains its stability from the newly formed C-C bond. WHEN CN- IS THE NUCLEOPHILE, CYANOHYDRINS ARE FORMED. |
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What is a condenstion reaction?
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A reaction in which water is lost between two molecules.
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What is the aldol condensation reaction?
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In the aldol condenstion, aldehydes act as nucleophile and target.
When ethanal (acetaldehyde) is treated w/ a base (OH-), an enoate ion is produced. The nucleophilic enolate ion can react w/ the carbonyl group of another acetaldehyde molecule. The product is 3-hydroxybutanal - This compound is called an aldol, from ALDEhyde and alcohOL. A nucleophilic addition rxn A base such as NaOH or KOH is added to an aldehyde. |
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What is the Wittig reaction?
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The Wittig reaction is a method of forming carbon-carbon double bonds by converting aldehydes and ketones into alkenes.
First step involves rxn of an alkyl halide with the nucleophile (C6H5)3P, triphenylphosphine. THE WITTIG REACTION ULTIMATELY CONVERTS C=O TO C=C. |
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What is the Wolff-Kishner reaction?
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Completely reduces aldehydes and ketones to alkanes.
Catalyzed by H2NNH2. Performed in basic solution and, therefore, is only useful when the product is stable under basic conditions. |
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What is the Clemmensen reduction reaction?
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Method of fully reducing aldehydes and ketones to alkanes.
Catalyzed by amalgamated zinc (HgZn) in hydrochloric acid (HCl) Not subject to the restriction of the Wolff-Kishner reaction which can only be performed under basic conditions. |
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Carboxylic acids are compounds that contain what functional group?
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Carboxyl group - A hydroxyl group attached to carbonyl groups.
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Nomenclature of carboxylic acids
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IUPAC - named by adding the suffic -oic acid to the alkyl root.
Carboxyl group receives the lowest possible number. Cyclic carboxylic acids are usually named as cycloalkane carboxylic acids. |
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Carboxylic acids are polar/nonpolar?
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Polar, therefore they can form hydrogen bonds.
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What are dimers? Can carboxylic acids form dimers?
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Dimers are pairs of molecules connected by hydrogen bonds.
Carboxylic acids can form dimers due to their polarity and therefore ability to hydrogen bond. |
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Describe the boiling point of carboxylic acids.
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Boiling points of carboxylic acids are higher than corresponding alcohols due to their ability to hydrogen bond and form dimers.
Boiling point follows usual trend and increases w/ molecular weight. |
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What causes the acidity of carboxylic acids?
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The acidity of carboxylic acids is due to the resonance stablization of the carboxylate anion (the conjugate base).
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What effect can substituents, such as electron-withdrawing groups, have on the acidity of a carboxylic acid?
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Substituents on carbon atoms adjacent to a carboxyl group can influence acidity.
Electron-withdrawing groups, such as -Cl or -NO2, further delocalize the neg. charge and increase acidity. Electron-donating groups, such as -NH2 or -OCH3, destablize the neg. charge, decreasing acidity. |
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How can you increase the acidity of a carboxylic acid?
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To increase the acidity, the negative charge needs to be stabilized.
Electron-withdrawing groups, such as -Cl or -NO2, further delocalize the neg. charge and increase acidity. Can also add groups that allow more resonance stabilization, such as benzyl or allyl substituents. The more of such groups that exist and the closer to the acid they are, the stronger the acid |
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How can you decrease the acidity of a carboxylic acid?
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Electron donating groups, such as -NH2 or -OCH3, destabilize the negative charge, decreasing the acidity.
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Describe the acidity of dicarboxylic acids.
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In dicarboxylic acids, one -COOH group is electron withdrawing and incluences the other, making the compound more acidic than the analogous monocarboxylic acid.
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Carboxylic acids can be prepared via oxidation of what groups?
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Aldehydes, primary alcohols, and certain alkylbenzenes.
Oxidant is usually KMnO4 (potassium permanganate). Secondary and tertiary alcohols can't be oxidized b/c of valence limitations. |
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Nitriles contain what functional group?
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-CN
Nitriles are also called cyanides. |
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Nitriles, compounds containing the functional group -CN, can be hydrolyzed to what product(s)?
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Carboxylic acids and ammonia or ammonium salts.
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Describe the hydrolysis of nitriles.
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Nitriles, or cyanides, contain the functional group -CN.
The cyanide anion CN- is a good nucleophile and will displace primary and secondary halides in typical Sn2 fashion. Can occur under acidic or basic conditions and the products are carboxylic acids and ammonia or ammonium salts. |
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When long-chain carboxylic acids react w/ sodium or potassium hydroxide, what is the product?
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Salts called soaps are formed.
RCOOH + NaOH --> RCOO-Na+ (a soap) + H2O These soaps possess a nonpolar "tail" and a polar carboxylate "head" so they are able to solubilize nonpolar organic compounds. |
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RCOOH + NaOH --> ?
RCOO-Na+ is called a soap. R is the nonpolar "tail", COO-Na+ is the polar carboxylate "head". |
RCOO-Na+ + H2O
RCOO-Na+ is called a soap. R is the nonpolar "tail", COO-Na+ is the polar carboxylate "head". |
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When placed in aqueous solution, soap molecules arrange themselves in what structure?
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Spherical structures called micelles.
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Carboxylic acids can be reduced to an alcohol using what reagent?
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LiAlH4 (lithium aluminum hydride)
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Carboxylic acids react w/ alcohols under acidic conditions to form what?
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Esters and water
In acidic solution, the O on the C=O can become protonated, accentuating the polarity of the bond, making the C even more susceptible to nucleophilic attack. |
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How are esters formed from carboxylic acids?
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Carboxylic acids react w/ alcohols under acidic conditions to form esters (also water).
In acidic solution, the O on the C=O can be protonated, accentuating the polarity (more + on C), making the C more susceptible to nucleophilic attack. This condensation rxn occurs most rapidly w/ primary alcohols. |
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Protonating the O on a C=O bond has what effect?
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Can happen under acidic conditions.
Accentuates the polarity of the bond (more + on the C), making C more susceptible for nucleophilic attack. Esters are formed from carboxylic acids this way. |
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What is an acyl halide?
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Compounds w/ carbonyl groups bonded to halides.
Also called acid halides. |
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Reacting a carboxylic acid with SOCl2 (thionyl chloride) will result in what product formation?
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Acyl halide, or acid halide formation.
(Acyl halide is a compound w/ carbonyl groups bonded to halides). |
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Describe decarboxylation of a carboxylic acid.
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When carboxylic acids are decarboxylated, they lose a carbon dioxide.
The carboxyl group is lost and replaced w/ a hydrogen. (Decarboxylation is very common in biochemical pathways in the body, such as the Krebs cycle). |
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Carboxylic acids can be converted into several types of derivatives. What are they?
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Acyl halides
Anhydrides Amides Esters |
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What is an acyl halide?
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A carboxylic acid derivative in which the -OH of the carboxyl group has been replaced w/ -X.
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What is an anhydride?
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A carboxylic acid derivative in which the -OH of the carboxyl group has been replaced w/ -OCOR.
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What is an amide?
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A carboxylic acid derivative in which the -OH of the carboxyl group has been replaced w/ -NH2.
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What is an ester?
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A carboxylic acid derivative in which the -OH of the carboxyl group has been replaced w/ -OR.
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What is the order of reactivity of the carboxylic acid derivatives?
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Acyl halides > anhydrides > esters > amides
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If any of the carboxylic acid derivatives undergo hydrolysis (water as the nucleophile), what is the product?
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The original carboxylic acid
(Hydrolysis is a type of nucleophilic substitution rxn in which water is the nucleophile) |
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Most common acyl halide?
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Acid chlorides
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How can you synthesize an acyl halide?
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Rxn of the carboxylic acid w/ SOCl2 (thionyl chloride).
Produces SO2 and HCl as side products. Alternatively, PCl3 or PCl5 will accomplish the same transformation. PBr3 can be used to produce an acid bromide. |
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If you react a carboxylic acid w/ PBr3, what is the product?
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An acid bromide (A type of acyl halide).
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What is a hydrolysis rxn?
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Cleavage by water
Hydrolysis = hydro + lysis "water" "cleavage" |
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How can you convert an acyl halide into an ester?
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Rxn w/ alcohols
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If you react an acyl halide w/ an alcohol, what is the product?
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Ester
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How can you convert an acyl halide into an amide (RCONH2)?
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React the acyl halide w/ an amine (R-NH2).
The side product is ammonium chloride (NH4Cl). |
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Describe the mechanism of a Friedel-Crafts Acylation on an aromatic ring
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The mechanism is electrophilic aromatic substitution.
The attacking reagent is an acylium ion, formed by rxn of an acid chloride w/ AlCl3 or another Lewis Acid. The product is an alkyl aryl ketone. |
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How can you convert an acid halide to an aclohol?
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This requires reduction.
Catalytic hydrogenation (H2 on Pd/BaSO4) will acomplish this. If in the presence of quinoline, the acid halide will stop at the intermediate aldehyde. |
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These molecules are condensation dimers of carboxylic acids w/ the general formula RCOOCOR.
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Anhydrides
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How are anhydrides synthesized?
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Anhydrides are formed by 2 acid molecules condensing (losing water).
Anhydride means "without water" Can also be formed by rxn of an acid chloride w/ a carboxylate salt (RCOO-). |
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How can you form a cyclic anhydride?
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Heating carboxylic acids
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If an anhydride is reacted w/ ammonia, what is the product?
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Amides and ammonium carboxylates
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To convert an anhydride to an amide, what reagent should the anhydride be reacted w/?
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Ammonia will cleave anhydrides producing amides and also ammonium carboxylates (R-COO-NH4+)
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What is spectroscopy?
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The process of measuring the energy differences b/t the possible states of molecular system by determining the frequencies of electromagnetic radiation (light) absorbed by molecules.
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What is infrared (IR) spectroscopy?
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IR spectroscopy measures molecular vibrations, which include bond stretching, bending, and rotation.
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What are the useful a absorption of infrared light regarding IR spectroscopy?
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The useful absorptions of infrared light occur in the 3,000-30,000 nm region, which corresponds to 3,500-300 cm^-1 (called wavenumbers).
When light of these wavelengths/wavenumbers is absorbed, the molecules enter higher (excited) vibrational states. |
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2 types of bond stretching:
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Symmetric
Asymmetric |
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What type of molecular vibration involves the largest change in energy? What region is it observed in?
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Bond stretching involves the largest energy change.
Observed in the 1,500 - 4,000 cm^-1 region. |
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What is necessary for absorption to occur?
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For absorption to be recorded, the motion must result in a change in a bond dipole moment.
Molecules comprised of atoms w/ the same electronegativity, as well as symmetrical molecules, do not experiance a changing dipole moment and, therefore, do not exhibit absorption. For example, O2 and Br2 do no absorb, but HCl and CO do. |
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Alcohols absorption frequencey IR absorption?
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3100-3500
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Aldehyde absorption frequency IR absorption?
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2700-2900 for (O)C-H
1725 - 1750 for C=O |
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Ketone absorption frequency IR absorption?
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1700-1750
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Alkane absorption frequency IR absorption?
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2800-3000
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NMR?
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Nuclear Magnetic Resonance.
Used to study protons (H+) and carbon-13 nuclei. But any atom possessing a nuclear spin (any nucleus w/ an odd atomic number or odd mass number) can be studied. |
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How do you read an NMR spectrum?
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Each peak represents a single proton or a group of equivalent protons. The number of peaks represents the number of nonequivalent protons.
Protons which are deshielded, or have electromagnetic atoms near them, resonate downfield. Electron-donating atoms shield the H nuclei, causing them to resonate upfield. "Downfield is DEshielded" |
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What is coupling and splitting regarding NMR?
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If 2 magnetically different protons are w/in 3 bonds of each other, this occurs.
The splitting of a peak represents the number of adjacent hydrogens. A peak will be split into n+1 peaks, where n is the number of adjacent hydrogens. |
