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53 Cards in this Set

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What does solvent extraction exploit?
exploits the particular solubilities of organic compounds in various solvents. Allows the chemist to separate a substance froma mixture of substances by adding a solvent that the cmopound of interest is highly soluble in.
distribution (or partition) coefficient
Ratio of the substance's solubilities in the two solvents is called the distribution (or partition) coefficient: Kd=Ca/Cb
Explain what the simplest liquid extraction is.
What is it good at removing?
simplest liquid-liquid extraction is accomplished when an organic compound is extracted with water b/c it removes substrances that are highly polar or charged like inorganic salts, strong acids and bases, and polar, low MW compounds (less than 5 carbons) such as alcohols, amines, and carboxylic acids.
What can organic compounds that are basic (sa. amines) be extracted from?
Organic compounds that are basic (ie. Amines) can be extracted from mixtures of organic compounds upon treatment with dilute acid (usually 5-10% HCl).
Explain the process of extraction of organic amines.
- This treatment will protonate the basic functional group, forming a positively charged ion.
- Resulting cationic salts of these basic compounds are usually freely soluble in aqueous solution and can be removed from the organic compounds that remain dissolve in the organic phase.
Isomer
same molecular formula, different structure
Constitutional isomers
different bond connectivity
stereoisomers
same bond connectivity, different spatial arrangement of atoms
Enantiomers
Non-identical mirror images (chiral molecules)
Meso
contains chiral centers and an internal plane of symmetry
diastereomers
stereoisomers that aren't enantiomers
geometric isomers
diastereomers that differ in orientation of substituents around a ring or double bond
epimers
diastereomers that differ in absolute configuration at only one chiral center
anomers
epimers that form as a result of ring cluser.
Compare the reactivity of R-X's for E1 and E2 reaction and reasoning.
Both E1 and E2 prefer tertiary the most.
E1: 3 > 2 >> 1 (b/c of carbocation stability)
E2: 3 > 2 > 1 (due to product stability)
What is the role of solvent in E1 and E2 reactions?
- E1 reactions are favored by protic (hydrogen bonding) solvents. (This stabilizes the carbocation).
- E2 reactions are favored by polar, aprotic (non-hydrogen bonding) solvents.
Compare the product compositions of E1 and E2 reactions.
- E1 reaction: more substituted alkenes are favored over less substituted ones.
- E2 reaction: Alkene stereochemistry is determined by the anti arrangement of the beta-proton and the leaving group.
What are the intricacies of the E2 reaction in terms of which proton is removed?
E2 rxns works best if the proton to be removed is anti to the leaving group, similar to the way the nucleophile must approach from the backside in an SN2 rxn. Since the rxn occurs in a single step and with the beta-proton anti to the LG, the stereochemistry of the dbl bond is determined by the rxn transition state.
What are the kinetics of an E1 and E2 rxn.
E1: reaction rate=k[haloalkane]
E2: reaction rate=k[base][haloalkane]
What are the conditions of an E1 and E2 rxn?
E1: 1st order elimination rxns are favored over substition rxns by the use of weak bases and high temperatures.

E2 conditions: Elimination rxns are favored over substition rxns by the use of strong bases and high temperatures.

Generallyh speaking, strong bases such as -OH and -OR yield exclusively the elimination product(s).
Compare the reactivity of R-OH's in an SN1 and SN2 rxn.
SN1: 3 > 2 >> 1 (due to stabilization of the carbocation)

SN2: 1 > 2 >> 3 (b/c of steric hindrance)
Compare the rearrangements of an SN1 and SN2 rxn.
SN1: carbocation rearrangement is possible. if the carbocation can rearrange to one that is more stable, it will.

SN2: Not possible, because carbocations aren't present in the reaction
Compare the role of the solvent in SN1 and SN2 rxns.
SN1: SN1 rxns are favored by protic (hydrogen bonding) solvents (this stabilizes the carbocation.)

SN2: Sn2 rxns are favored by polar, aprotic (non-hydrogen bonding) solvents.
Compare the role of the stereochemistry in SN1 and SN2 rxns.
SN1: Almost complete racemization due to nucleophilic attack on either side of p orbital. However, usually a little net inversion due to ransient sheilding of LG. Net inversion increases with increasing solvent polarity.
SN2 rxns: Complete stereochemical inversion of the carbon that is being attacked by the nucleophile.
Compare SN1 and SN2 kinetics.
SN1: rxn rate = k[electrophile]

SN2: rxn rate = k[nucleophile][electrophile]
If the resonance contributors are similar in that they are equally stable, what would you expect?
That they produce equal % products.
If a product has a greater portion of the products produced, then how does this relate to its activation energy?
Its activation energy should be lower than that of the other products.
- what is a conjugated system? - which is more stable, conjguated or unconjugated
- molecules having alternating double bonds - more stable than unconjugated system because it has resonance
- Heat of hydrogenation; - Is something with greater heat of hydrogenation more stable or less stable?
- Heat released upon the addition of H2 to one mole of a compound (to generate the corresponding alkane) - this will usually be an exothermic process - both starting material and products are organic compounds - Greater heat of hydrogenation for same molecular formula, it is LESS STABLE
Endothermic reaction
Heat is absorbed during this process (heat taken in)
Exothermic reaction
heat released (heat give out)
Heat of Combustion
Heat released when one mole of a compound undergoes complete combustion in O2. - combustion (released CO2 and H2O) usually exothermic process - the organic compound is a starting material for teh reaction
Heat of Formation
- heat released if one mole of a compound were formed from its component elements in their standard state - can be either endothermic or exothermic process - important to make sure they are balanced when drawing diagrams. - the organic compound is a product for the reaction
Is something with greater heat of hydrogenation more stable or less stable?
- Greater heat of hydrogenation for same molecular formula, it is LESS STABLE
(T/F) Iodine in the presence of UV light will break up into radicals that can abstract hydrogens.
FALSE. It will break up into radicals but it has great difficult abstracting hydrogens. - Iodine is often used as a free-radical inhibitor b/c it will readily react with other radicals. IODINE INHIBITS REACTIONS, IT RARELY INITATES THEM
After radical intiaitoin step by UV light, what would slow down or stop the halogenation reaction?
water b/c it prevents propagation by mopping up the bromine radical
What is not an example of a conjugated system: a. benzene b. 1,3-cyclohexadiene c. 1,2-butadiene d. cyclobutadiene
1,2 butadiene. (draw it out)
What happens when an alkene is reacted with H2O, H+/heat?
The OH goes to the more substituted markovnikov.
Will alkanes be substitued by a bromide from hydrogen bromide?
No alkanes are hihgly unreactive molcuels alkanes which will only undergo substitution when extreme conditions are employed -=- like UV light for instance. UV light will initiate highly reactive free radicals which will now react. (Br2 will also work with hv to get radical rxn with alkanes)
glucoside
a carbohydrate in its acetal or ketal form, in which the anomeric hydroxyl group is replaced with an alkoxy group. (oxygen attached to another monosaccharide or a simple alkyl group)
- glucoside bond
- alpha-glucoside linkage
- one in which the glucose subunit is attached to an alkoxy group
- alpha correponds to the downwards or axial orientation of the hydroxyl group on the anomeric carbon. In summary: look for a linkage btw glucose and its acetal group which is oriented axially or downward on the page.
Benedict's reagent
used to test for reducing sugars; in other words, those sugars that contain hemiacetal or hemiketal groups.
- when it reacts with the reducing sugar, a brick-red copper oxide precipitate is formed -- characteristic of a postive test.
- reaction only occurs when himacetals and hemiketals exist in equilbrium with their open chain forms.
carbonyl group
C=O
Does glucose have a carbonyl group?
Yes.
Do some dissacharides possess free hemiacetal and himketal groups?
Yes, maltose consists of two glucose residues, one of which is present in the hemiacetal form.
alpha-anomers
defined as those in which the hydroxyl group on the anomeric carbon in the ring is oriented AXIALLY. (straight up or down)
Mutarotation
- the change in specific rotation that occurs when an α (alpha) or β (beta) hemiacetal form of carbohydrate is converted into an equilibrium mixture of the two forms.
- also refers to the interconversion between the α and β forms.
- Is sucrose a reducing sugar?
- Is fructose, glucose, glyceraldehyde, lactose, arabinose, and maltose reducing surgars?
- No.
- Yes.
What is a reducing sugar?
- A reducing sugar occurs when its anomeric carbon is free, which is the chiral carbon.
- ANy sugar that contains a hemi-acetal wil lbe a reducing sugar
- Reducing agent: element or a compound in a redox reaction that reduces another species. In doing so, it becomes oxidized and is therefore the electron donor in the redox.
Reducing agent;
- Reducing agent: element or a compound in a redox reaction that reduces another species. In doing so, it becomes oxidized and is therefore the electron donor in the redox.
- 2Mg(s) + O2 => 2Mg2+(s) + 2O2-
here Mg(s) is the reducing agent... O2 is being reduced.
What makes a strong reducing agent?
- A strong reducing agent is one which loses or donates electrons easily.
- Nucleus in an atom is the main force pulling the electrons inwards, keeping them from going anywhere. ==> if atomic radius is large, infludence of the nucleus is not sufficient.
==> Elements with large atomic radii are strong reducing agents since no significant force keeps them from releasing electrons easily.
- Reducing agents can be ranked by increasing strength by ranking their oxidation potentials: strongest when it has a more postiive oxidation potential and will be week reducing agent whenever it has a negative oxidation potential. (in order to tell, change sign if in reduction potential)
Nucleophile
describes the tendency of an electron rich species to be attracted to the positive nuclear charge of an electron poor species, the electrophile .
Nucleophilicity trends (compared with basicity)
1) Across a row in the periodic table nucleophilicity (lone pair donation) C- > N- > O- > F- since increasing electronegativity decreases the lone pair availability. This is the same order as for basicity.
2. If one is comparing the same central atom, higher electron density will increase the nucleophilicity,
e.g. an anion will be a better Nu (lone pair donor) than a neutral atom such as HO- > H2O. This is the same order as for basicity.
3. Within a group in the periodic table, increasing polarisation of the nucleophile as you go down a group enhances the ability to form the new C-X bond and increases the nucleophilicity, so I- > Br- > Cl- > F-. The electron density of larger atoms is more readily distorted i.e. polarised, since the electrons are further from the nucleus.
Note that is the opposite order to basicity (acidity increases down a group) where polarisability is much less important for bond formation to the very small proton.