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71 Cards in this Set
- Front
- Back
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Define the following:
- Structural isomers - Conformational isomers - Diastereomers - Enantiomers - Geometric isomers |
- Structural isomers: share only formula
- Conformational isomers: differences stem from rotation around a single bond - Diastereomers: wedge where a dash would be in the other - Enantiomers: mirror images - Geometric isomers: cis vs. trans around a double bond |
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How do you determine S vs. R for a chiral center?
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Orient so that H is going into the page; label from highest priority (electronegativity to lowest); if proceeds clockwise it's R; if proceeds counterclockwise it's S
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What are dextrorotatory and levorotatory compounds?
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In optical activity (enantiomers differ in optical activity), compounds that bend light to the right (from perspective of viewer looking at light coming at them) are called dextrorotatory; those that bend light to the left are levorotatory
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When does a molecule have optical activity?
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When it as no plane of symmetry; mesocompounds are chiral, but have a plane of symmetry
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Describe the four types of conformational isomers.
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- Staggered: methyls are 180° apart (anti); lowest E state
- Gauche: methyls are 60° apart - Eclipsed: methyls are 120° apart - Totally eclipsed: methyls overlap; highest E state |
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Why do cyclohexanes adopt nonplanar conformations?
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Reduce angle strain, torsional strain, and nonbonded strain (van der Waals repulsion)
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Are axial or equatorial groups favored in chair cyclohexanes?
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Equatorial, because of steric repulsion with other axial substituents
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What is the hybridization of single, double, and triple bonds?
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Single: sp3
Double: sp2 Triple: sp |
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What is a primary carbon?
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A carbon bonded to only one other carbon atom
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What are the effects of chain length and branching on b.p, m.p, and density?
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Increasing chain length increases b.p, m.p, and density; increasing branching decreases b.p, m.p, and density
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What is combustion?
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Combination of an alkane with oxygen to form CO2, H2O, and heat
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What is pyrolysis?
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Cracking; breaking down of a molecule (such as an alkane) by heat, producing two free radicals, which then combine as smaller molecules
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What is disproportionation?
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A chemical reaction (reversible or irreversible) in which a species is simultaneously reduced and oxidized so as to form two different products; transfer of a hydrogen from one radical to another, leaving one as a non-radical double bonded compound and the other as a non-radical
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What is the rate determining step of an SN1 reaction?
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Formation of carbocation
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What is the difference between an SN1 and an SN2 reaction?
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In SN1, dissociation of molecule into carbocation, then nucleotide attacks; in SN2, nucleotide attacks directly, forming a trigonal bipyramidal transition state
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What does the rate of SN2 depend on?
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Concentration of two reactants (so second order)
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Do higher melting and boiling points indicate increased or decreased stability?
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Increased
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Do trans alkenes have higher or lower melting points than cis?
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Higher, because their greater degree of symmetry allows them to pack more tightly
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Describe E1 eliminations.
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Step 1: Leaving group departs, forming a carbocation
Step 2: Proton is removed by a base |
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What are 4 conditions that favor E1 and SN1?
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1. Highly polar solvents
2. Highly branched carbon chains 3. Good leaving groups 4. Weak nucleophiles in low concentrations |
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Are strong Lewis Acids electrophiles or nucleophiles?
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Electrophiles
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Whatis Markovnikov's rule?
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When HX adds to a double bond in alkene, H adds to C with more H and X adds to C with fewer H.
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What is Hückel's rule?
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Aromatics must contain 4(n)+2 pi electrons, where the number of pi electrons = twice the number of double bonds; otherwise it is anti-aromatic
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What are the configurations for ortho, meta, and para benzene rings?
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ortho: 1,2
meta:1,3 para:1,4 |
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Give the effects of the following substituents on aromatics:
NH2, NR2,OH, NHCOR, OR, OCOR, R, halogens, NO2, SO3H, carbonyl compounds |
NH2, NR2,OH, NHCOR, OR, OCOR, R: activating, ortho/para-directing (e- donating ~ decrease susceptibility to nucleophilic attack)
Halogens: deactivating, ortho/para-directing NO2, SO3H, carbonyl compounds: deactivating, meta-directing (e- withdrawing ~ increase susceptibility to nucleophilic attack) |
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Can carboxylic acids form hydrogen bonds?
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Yes
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Describe the boiling points of carboxylic acids.
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Higher than those of corresponding alcohols, because they can form hydrogen bonds.
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Describe the boiling points of ketones.
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Elevated, because O is electronegative forming dipoles; not as high as alcohols, because no H
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Are halides electron-donating or withdrawing?
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Withdrawing
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What type of amines can form H bonds?
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Primary and secondary; tertiary can't, so has a lower b.p.
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What happens to b.p. as molecular weight increases?
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B.p. increases
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What is the formula for ammonia?
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NH3
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What is the effect of electron-donating groups (such as -OH, CH3, and -NH2) and electron-withdrawing groups (such as NO2) on anilines?
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Electron-donating increase basicity; electron-withdrawing decrease basicity
http://www.mhhe.com/physsci/chemistry/carey/student/olc/graphics/carey04oc/ref/ch12substituenteffects.html |
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What is extraction?
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Transfer of a dissolved compound from one solvent into another in which it is ore soluble; most impurities will be left behind; two solvents should be immiscible and temporarily mixed together so the solute can transfer
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What device is used for extraction?
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Separatory funnel
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What is gravity filtration/vacuum filtration?
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Substance is dissolved in a solvent and flow through filter paper, leaving behind impurities
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What is recrystallization?
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Impure crystals are dissolved in a minimum amount of hot solvent; as solvent is cooled, crystals reform, leaving impurities in solution; solvent must be able to dissolve impurities at both temperature, but only solid while it is hot
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What is distillation?
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Separation of one liquid from another; the one with the lower boiling point evaporates, condenses, and then collects
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What is the difference between simple and vacuum distillation?
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Simple separates liquids that boil below 150°C; vacuum separates those that boil above (reduces pressure which lowers boiling points)
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Does increased pressure increase or decrease boiling point?
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Increase, because pushes molecules close together
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What is fractional distillation?
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Used for liquids with b.p. below 25°C; has beads inside where collects and then re-evaporates; as get higher,have greater portion of lower b.p. liquid
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Is the silica plate in chromatography polar or nonpolar?
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Polar, so nonpolar substances travel faster/higher
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What are vapor-phase chromatography and HPLC?
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30-foot column with absorbant; pass vapors through, which travel at different rates, because adhere to absorbant differently; HPLC is same, but with liquid pass through under high pressure
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What type of gels are used to separate nucleic acid and proteins?
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Agarose is used to separate nuclei acid; SDS is used to separate proteins
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Describe the peaks for the following in infrared spectrum:
- Alcohols - Aldehydes - Ketones - Acids - Amines |
- Alcohols: 3,100-3,500 (broad)
- Aldehydes: 2,700-2,900; 1,725-1,750 - Ketones: 1,700-1,750 (sharp) - Acids: 1,700-1,750; 2,900-3,300 (broadest) - Amines: 3,100-3,300 (sharp) |
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How does NMR work?
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In magnetic field, α are oriented with field and β are against; when energy applied, some will be excited to β; this energy of excitement can be detected
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What are the units of NMR
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Parts per million (ppm), which represent 'chemical shift'
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Is downfield more shielded or deshielded?
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Downfield (higher ppm) is more deshielded
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Describe coupling.
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In NMR, if a protein is within 3 atoms from another proton (first proton is 0, two atoms can be in between, second proton is 3), then the spins can affect each other; if 0 adjacent H, 1 peak, if 1, then there are two (reflecting the second H either having α or β spin); if 2, then 3 peaks, etc.
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Describe 13C NMR.
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Same as HNMR, except coupling is only observed for H attached to C; this can be spin-decoupled,however, so there are not multiple peaks due to coupling
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What is mass spectrometry?
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Sample ionized by high-speed beam of electrons; particle accelerator puts them in flight, magnetic field deflects them, detector records how much they were detected based on their weight; can be used to distinguish between particles based on mass that IR couldn't
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What is the difference between an aldose and a ketose?
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Aldose is an aldehyde sugar; ketose is a ketone sugar
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Describe D and L configurations of sugar.
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If OH is on the left on highest numbered chiral center (that farthest from the carbonyl), then it's L
http://universe-review.ca/I11-10-Lglucose.jpg |
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What are pyranose and furanose rings?
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Pyranose are six-membered carbohydrate rings; furanose are five-membered carbohydrate rings
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What are cellulose and starch repeating units of?
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- Cellulose is D-glucose linked by 1,4-β bonds
- Starch is glucose linked by 1,4-α bonds |
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Describe titration of amino acids.
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2 moles of base must be used to deprotonate one mole of amino acid; first mole deprotonates carboxylic group; second deprotonates amino group
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What are 8 nonpolar amino acids?
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Alanine, valine,leucine,isoleucine, proline, phenylalanine, glycine,tryptophan
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What are 7 polar amino acids?
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Methionine,serine, threonine, cysteine, tyrosine, asparagine,glutamine
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What are 2 acidic amino acids?
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Aspartic acid, glutamic acid
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What are 3 basic amino acids?
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Arginine, lysine, histidine
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What are conjugated proteins?
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Derive part of their function from covalently attached molecules called prosthetic groups, which may be organic molecules or metal ions
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What is a ketal?
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An acetal
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What is one method to open an epoxide ring?
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Add acid and a nucleophile, such as water
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How do you add an SO3H group to a benzene ring?
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Mix benzene with SO3 and H2SO4
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What conditions suit E1 well?
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The same that suit SN1 well.
(High branching suits E1 and SN1, because it creates stable carbocations) |
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Is cyanide (CN) a good leaving group?
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No
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What is pl?
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Isoelectric point; the pH at which an amino acid contains equal amounts of the positively and negatively charged forms so that the overall amino acid is neutral
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What is the elution volume?
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The point on the pH gradient where the pH is high enough to cause a change in the charge on the molecules
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How can an alcohol be dehydrated (lose the OH group)?
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Heating in an acidic solution (H adds onto the OH to form an oxonium ion (OH2), which can then be removed, leaving a carbocation)
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Are more or less substituted carbocations conducive to forming double bonds?
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More substituted, because the electron-donating alkyl groups help to stabilize the double bond
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Do acids that contain an electron-withdrawing substituent on the alpha carbon tend to be stronger or weaker?
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Stronger, sinc ehte dissipation of electron density has a stabilizing effect on teh carboxylate anion
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