Mcat Ochem - Tl

Front 1

inductive effects vs. resonance effects

Back 1

inductive effects = stabilize charge through sigma bonds

resonance effects = stabilize charge by delocalization through pi bonds

Front 2

Degree of Saturation

Back 2

saturated if it contains no pi bonds and no rings

Front 3

Rank the stability of Carbocations and carbanions.

Back 3

For carbocations:

Stability: 3 > 2 > 1 > methyl

Reactivity and energy: methyl > 1 > 2 > 3

For carbanions, the trends are opposite.

Front 4

conjugated system

Back 4

3 or more atoms that each bear a p orbital

Front 5

Name 3 basic principles of resonance delocalization.

Back 5

1. atoms that are truly sp3 hybridized cannot be part of resonance

2. typically involve electrons that are adjacent to a pi bond or an unhybridized orbital

3. Resonance structures of lowest energy are the most important.

Front 6

What are the three main criteria for ranking resonance structure stability?

Back 6

1. octet rule is satisifed for ALL atoms

2. separation of charge is minimized

3. If structures have formal charge, negative charges are on more electronegative atoms and positive charges are on the less electronegative atoms.

Front 7

Nucleophilicity = measure of how "strong" a nucleophile is

What are the general trends for relative nucleophilicities?

Back 7

1. Nucleophilicity increases as negative charge increases.

2. Nucleophilicity increases going down the periodic table within a particular group.

3. Nucleophilicity increases going left in the period across a particular period.

Front 8

Electrophilcity = measure of how strong an electrophile is

Back 8

electron pair acceptors also known as Lewis acids

Examples of strong electrophiles include: tertiary carbocation, BH3, H+

Front 9

What will treating the following reactants with H2 in a solution of Ni w/ heat form?

1) cyclopropane

2) cyclobutane

3) cyclopentane

4) cyclohexane

Back 9

1) propance

2) butane

3) no reaction

4) no reaction

Front 10

Conformational Isomers

Why are staggered conformations more stable than eclipsed conformations?

Compare the stability of anti, guache, and syn conformation.

Back 10

differ by rotation around a sigma bond

staggered conformations minimize the effects of electronic repulsion and minimizes steric hindrance

Stability Generally in the absence of H bonding and if the 2 groups are NOT large:

anti (2 largest group 180 degrees apart) > guache (2 largest group 60 degrees apart) > syn (2 largest group overlap)

Front 11

Constituational Isomers

Back 11

Differ in bond connectivity

e.g. pentane, isopentane, neopentane

Front 12

Stereoisomers

Back 12

same bond connectivity, different spatial arrangements of atoms

Front 13

Enantiomers vs. Diastereomers vs. Meso Compounds

Back 13

Enantiomers are non-identical mirror images whereas Meso Compounds are identical mirror images.

Diastereomers are stereoisomers that are not enantiomers.

Front 14

Geometric Isomers vs. Epimers vs. Anomers

Back 14

geometric isomers are diastereomers that differ in orientation of substituents around a ring or a double bond

Epimers are diastereomers that differ in absolute configuration at a single chiral center -> if this chiral center is due to ring closure then it in anomer (either beta or alpha)

Front 15

What is used to extract the following:

1) organic amines

2) carboxylic acids

3) phenols

dissolved in diethyl ether

Back 15

1) dilute acid (e.g. 5-10 % HCl)

2) dilute base (e.g. 5 % NaHCO3 or NaOH)

3) NaOH

Front 16

Mass Spectrometry

Back 16

determine the mass of compounds in a sample

Output is a graph of abundance versus M/e (Mass over charge (typically e is + 1))

Front 17

UV Spectroscopy

What are the two classes of mlcs that UV/Vis Spec is most useful for?

Back 17

1. complexes of tranisition metals

2. highly conjugated organic systems

Front 18

IR Spectroscopy

Back 18

organic compound is irradiated w/ infrared radiation

its covalent bonds will begin to vibrate at distinct energy levels

output is transmittance versus wavenumber (reciprocal of wavelength)

Front 19

Important IR Spec Stretching Frequencies

Back 19

Carbonyls: strong and sharp at 1700

Alkenes: strong and sharp at 1650

Triple bonds: 2260-2100

OH: 3600-3200

NH: 3150-2500

Front 20

Hydrogen NMR Spectroscopy

Back 20

equialent H = indentical electronic environments

spin-spin splitting phenomenon = interactions between nonequivalent hydrogens

integration = area under each peak is proportional to the relative # of protons giving rise to each peak

chemical shift = indicates location of the resonance (set of peaks) in the NMR spectrum

Front 21

Chemical Shift in NMR Spectroscopy

Back 21

1. electronegativity - more electronegative atoms will deshield causing downfield shift

2. Hybridization effect - greater the s-orbital character, the more deshielded

3. Acidity - acidic protons on a COOH are extremely deshielded (10-13 ppm)

4. H-bonding - causes a wide variation of chemical shifts

Front 22

Important/Common Hydrogen NMR chemical shift values

Back 22

Alkyl: 0 to 2

aromatic: 6.5 to 8

vinyl/alkene: 5 to 6

alcohol: 2-5

Front 23

List the key facts about an SN2 reaction.

Back 23

1. Reactivity of substrate: CH3 > 1 > 2 >>> 3 (steric hindrance)

2. inversion of stereochemistry due to backsided attack

3. reaction rate = k [nucleophile][electrophile]

4. no rearrangements of C backbone

5. favored when nucleophile is strong and non-bulky (e.g. NaI, NaN3, NaOH)

6. solvent: favored by polar, aprotic (non-hydrogen bonding) solvents

Front 24

List the key facts about an SN1 reaction.

Back 24

1. Reactivity: 3 > 2 > 1 (due to stabilization of the carbocation)

2. almost racemic mixture due to attac on either side of the p orbital

3. reaction rate = k [electrophile]

4. rearrangements of C backbone possible

5. favored by non-basic weaker nucleophiles

6. solvent: favored by aprotic (hydrogen bonding solvents as this stabilizes the carbocation

Front 25

What configurations are animal AAs in and what are naturally occurring carbohydrates in?

Back 25

Animal AAs are L configuration

Naturally occurring carbohydrates are D configuration

Front 26

What are the three classification systems for organizing amino acids and carbohydrates?

Back 26

1. (+) and (-) describe optical acitivity and mean the same thing as d and l

2. R and S describe actual structure or absolute configuration

3. D and L tell us the basic precursor of a mlc (e.g. D- or L- glyceraldehyde)

Front 27

What reagent is used to oxidize a primary alcohol into an aldehyde?

What if a stronger oxidizing reagent is used?

Back 27

PCC oxidizes a primary alcohol to an aldehyde.

Stronger oxidizing reagents result in a carboxylic acid.

Front 28

Why can tertiary alcohols not be oxidized to a carbonyl?

Back 28

Oxidizing reagents require removal of a hydrogen from the C. There is no such H on a tertiary alcohol.

Front 29

Draw keto-enol tautomerism.

Front 30

Racemization

Back 30

loss of defined stereochemistry at a once chiral alpha-C, resulting in a mixutre of R and S configurations

Front 31

What are comon reducing agents used in the reduction of carbonyls to alcohols?

Back 31

1. NaBH4 in EtOH

2. LiAlH4 in ether

these reagents readily lose electrons by adding hydride (H with pair of electrons) to the carbonyl

Front 32

Grignard reagents

Back 32

organometallic reagent used in a nucleophilic addition to a carbonyl carbon

to avoid unwanted protonation of the basic grignard reagent, an aprotic solvent is often used followed by an acid workup

R- M+

alcohol and COOH groups on the carbonyl containing mlc must be protected prior to adding the grignard reagent

Front 33

Mesolyates and Toslyates

Back 33

utilized in the protection of amino and OH groups rendering them inert for the subsequent reaction steps

functionality can be regained by workup with generally acidic conditions

Front 34

How are acetals formed?

Back 34

Aldehyde or ketone reacts with alcohol in the presence of acid.

if one equivalent of alcohol is present, rxn will stop at a hemiacetal

if more than 1 equivalent of alcohol is present rxn will go to acetal and water will be lost

Front 35

Imine Formation

Back 35

Aldehyde/ketone reacts with a primary amine in a weakly acidic condition

Front 36

Enamine

Back 36

Aldehyde/ketone reacts with secondary amine in a weakly acidic condition

forms a double bond from deprotonation of the alpha hydrogen

Front 37

Tips for Drawing Aldol Condensation Product

Back 37

1. Determine the electrophile, if there is a ketone or aldehyde with no alpha Hs it will be the electrophile.

2. Find the beta C on the nucleophile and attach all the substituents on the carbonyl of the electrophile minus the carbonyl.

3. Add OH to the beta C.

4. In the presence of heat, water will be lost in an elimination reaction to produce an alpha,beta unsaturated carbonyl.

Front 38

What reagent is commonly used to reduce Carboxylic acids to primary alcohols?

Will NaBH4 work?

Back 38

NaBH4 will not work.

LiAlH4 will reduce a carboxylic acid to a primary alcohol.

Front 39

What is the relative reactivity of the carboxlyic acid derivatives?

Back 39

acid chlorides > acid anhydrides > esters > amides

Front 40

Esterfication

Back 40

Alcohol + a carboxylic acid -> an ester

Front 41

In hemiacetal to acetal formation, what is necessary?

Back 41

a catalytic amount of acid is necessary to protonate the hemiacetal OH group so it can leave as water