Chem 215-1 Exam 2 Concept Review

What structures have a non-superimposable mirror image?

Chiral

What structures have a superimposable mirror image?

Achiral

When you can rotate an duplicate to make it look the same as an original reference, what is that called?

Superimposable

What hybridization of carbon is the only one capable of having a chiral center?

Sp3

Relationship where two things are non-superimposable mirror images of each other

Enantiomers

What configurations do you assign chiral centers?

R/S

When assigning R/S configurations, which atom should be oriented at the back?

Lowest priority (Usually H)

What does R designation mean?

Substituent priority decreases in priority clockwise for chiral center

What does S designation mean?

Substituent priority decreases in priority counterclockwise for chiral center

What is most important for determining priority?

Atomic number

As you take a mirror image…

All chiral centers flip R ←→ S

Relationship for configurational isomers that are not mirror images for each other

Diastereomers

Contains at least two chiral centers but has a plane of symmetry that makes it achiral overall

meso compound

What configurations do you assign alkenes?

E/Z

How do you determine E/Z configuration in a structure?

Find higher priority substituent on each carbon, then analyze positioning planewise

Configuration where the higher priority groups are on the same side of the double bond

Z

Configuration where the higher priority groups are on opposite sides of the double bond

E

N with lone pair bonded to three different substituents is achiral overall; why?

interconversion through rehybridization

What happens to enantiomers in chiral environments?

will have different chemical and physical properties

What happens to enantiomers in achiral environments?

will have the same chemical and physical properties

Diastereomers must have…

different physical and chemical properties in general

Who donates a proton (H+)?

Bronsted-Lowry Acid

Who accepts a proton (H+)?

Bronsted-Lowry Base

anything with an H…

can be an acid

anything with electrons (negative charge, lone pair, pi bond)…

can be a base

What are stronger acids more likely to do?

give up proton more easily

What are stronger bases more likely to do?

take a proton

Lower pKa corresponds with

better acid

Higher pKA corresponds with

worse acid

Lower pHs progress reactions in which direction?

Towards A- (usually right)

Higher pHs progress reactions in which direction?

Towards HA (usually left)

What does life favor?

Weaker acids

The acronym for reasoning about the strength of an acid (and thus base)?

CARDIN-al Rule

Strong acids create…

stabler bases

C in CARDIN-al

Charge

When analyzing charged vs charged, which one is usually stronger?

charged acid

When analyzing charged vs uncharged, which one is usually weaker?

uncharged acid

A in CARDIN-al Rule

Atoms the proton is connected to

What is the trend for atoms the proton is connected to?

stronger = more EN atom and larger atom (favored)

How does hybridization relate to acid strength?

Stronger acids have more s character because of e- density closer to nucleus

RD in CARDIN-al Rule

Resonance Delocalization

How does resonance relate to acid strength?

More resonance increases strength

IN in CARDIN-al Rule

Inductive Effects

How do acids with electron-withdrawing groups affect acid strength? (Inductive Effects)

Stabilize nearby negative charges whilst destabilizing nearby positive charges. Increases strength

How do acids with electron-donating groups affect acid strength? (Inductive effects)

Stabilize nearby positive charges whilst destabilizing nearby negative charges. Decreases strength

alcohol (-OH) pKA

16

carboxylic acid (C=OOH) pKA

4-5

phenol pKA

10

methane pKA

48

amine pKA

10.5

Why do we have metals in reactions?

Anions cannot exist in the solid or liquid phase alone

What roles do metals serve in reactions?

Spectator Ions

What has a metal atom bonded directly to a carbon atom?

Organometallic compound

What do organometallic compounds do?

Give carbon a negative formal charge when the metal is removed

Organometallic that has a C-C-Li arrangement (a bit more reactive than the other)

Organolithium

Organometallic with C-C-MgBr

Grignard reagent

Why do these reactions happen?

Products have better charge stability (WINS)/will have greater total bond energy

Attracted to nuclei/positive charge. Donates an electron pair to form a bond

nucleophile

Electron poor species that is “attached” by the nucleophile

Electrophile

The molecule where the action is taking place/stuff happens

Substrate

The thing that leaves. Takes electrons from the bond and usually ends up negatively charged

Leaving group

What are leaving groups usually?

EN atoms or things that are stable with negative charges

What happens in SN2 (Bimolecular Nucleophilic Substitution) and SN1?

nucleophile substitutes for a leaving group

What happens in E2 and E1?

Base takes H on adjacent C, form pi bond, leaving group leaves

What is coordination?

Bond forming; anion bonds to cation (pos charged C) of different species

In elementary steps, nucleophiles correspond with…

Lewis Base

In elementary steps, electrophiles correspond to

Lewis Acid

What is heterolysis?

Bond breaks and the two electrons end up on the leaving group

What is nucleophilic addition?

Nucleophile attaches to substrate, pi bond broken and electrons attach to substituent

What is nucleophilic elimination?

Leaving group leaves and becomes nucleophile, pi bond forms between substituent and carbon

What is electrophilic addition?

Nonpolar pi bond donates electrons to strongly electron-deficient electrophile and forms a new bond between the two (creates a carbocation)

What is electrophilic elimination?

electrophile eliminated from carbocation, generating a stable, uncharged, organic species

What is a carbocation rearrangement?

Stuff in a carbocation moves around to increase stability

Two kinds of carbocation rearrangement

1,2-Hydride shifts and 1,2-Alkyl shifts

How are carbocations distinguished?

By their degree of alkyl substitution

Order of increasing stability with alkyl substitution

methyl, primary, secondary, tertiary, resonance-stabilized

Example of bond-energy driven force at play

Keto-enol tautomerization

Keto-enol

form of ketones/aldehydes which exist in equilibrium under acid/base conditions

How does MO explain the concepts in this exam?

Bonds form when the HOMO of one unit and the LUMO of the other have decently significant overlap.

In a reaction coordinate diagram, what does the first dip in the graph correspond with?

Reactants

In a reaction coordinate diagram, what do the peaks in the graph correspond with?

Transition states

In a reaction coordinate diagram, what do the dips (excl. last one) in the graph correspond with?

Intermediates

In a reaction coordinate diagram, what does the last dip in the graph correspond with?

products

What is the rate determining step?

The highest energy barrier step

What is the rate for an E2 or SN2 reaction?

rate = k[nucleophile][substrate]

What is the rate for a SN1 or E1 reaction?

rate = k[substrate]

What is a racemic mixture?

50/50 mixture of R/S. Shows up with SN1