Organic Nucleophilic Substitutions and Eliminations

general nucleophilic substitutions proceed how

electron pair on nucleophile attacks carbon atom with a partial positive charge bound to an electronegative atom (leaving group)

nucleophiles are often BLANK charged

negatively

a 1 step nucleophilic reaction is called

bimolecular

bimolecular reactions are also reffered to as

Sn2

Sn2 reactions are

first order

2 step nucleophilic substitutions are called

unimolecular

unimolecular substitution reactions are also referred to as

Sn1

In an Sn1 mechanism, which step is rate determining?

ionization

In regards to what is an Sn1 ionization first order

alkyl substrate concentration

Identify the mechanism

Sn2

Identify the mechanism

Sn1

unimolecular reactions produce

racemized tetrahedral stereocenters bearing the nucleophile

bimolecular reactions happen via

inversion of configuration at carbon center

in nucleophilic elimination, the nucleophile acts as a

base

The removal of the acidic proton, and the departure of the leaving group produces a BLANK from the alkyl substrate

alkene

One step elimination reactions are referred to as

E2 mechanisms

Two step elimination reactions are referred to as

E1 mechanisms

Identify the mechanism

E2

Identify the mechanism

E1

The major product of a nucleophilic reaction is substitution if the leaving group is on a

primary carbon

The major product of a nucleophilic reaction is elimination if the leaving group is on a

tertiary carbon

bimolecular reactions are faster on BLANK carbon atoms

primary

unimolecular reactions are faster on BLANK carbon atoms

tertiary

If the alkyl substrate is secondary, and the nucleophile is a strong base, what is the dominant reaction

E2

If the alkyl substrate is secondary, and the nucleophile is a weak base, what is the dominant reaction

Sn2

If the alkyl substrate is secondary, and the nucleophile is poor, what is the dominant reaction

Slow Sn1/E1 in polar protic solvents

If the alkyl substrate is primary, and the nucleophile is a strong base, what is the dominant reaction

Sn2 (E2 with non-nucleophilic bases)

If the alkyl substrate is primary, and the nucleophile is a weak base, what is the dominant reaction

Sn2

If the alkyl substrate is primary, and the nucleophile is poor, what is the dominant reaction

no reaction

If the alkyl substrate is tertiary, and the nucleophile is a strong base, what is the dominant reaction

E2

If the alkyl substrate is tertiary, and the nucleophile is a weak base, what is the dominant reaction

Sn1/E1 in polar, protic solvents

If the alkyl substrate is tertiary, and the nucleophile is poor, what is the dominant reaction

Sn1/E1 in polar, protic solvents

Strong bases favor the elimination product from what carbon atoms

secondary and tertiary

Weak bases produce more BLANK products mostly via BLANK

substitution, unimolecular

Hindered bases favor a BLANK product in all degrees of carbon atoms

elimination

Rates of substitution and elimination reactions are favored by better

leaving groupsW

What makes a good leaving group?

weak bases

Protonation of a poor leaving group makes it a weaker base and therefore

a better leaving group

What mechanistic step is most common in all of organic chemistry

protonation

What reaction mechanism does the reaction coordinate diagram represent?

Sn1

What reaction mechanism does the reaction coordinate diagram represent?

Sn2

What reaction mechanism does the reaction coordinate diagram represent?

E1

What reaction mechanism does the reaction coordinate diagram represent?

E2

In an exothermic reaction, the energy of the products is

lower than the energy of the reactants

In an endothermic reaction, the energy of the products is

higher than the energy of the reactants

The # of peaks in a reaction coordinate diagram is equal to

number of mechanistic steps

The height difference between reactants and products on a reaction coordinate diagram represents the

change in enthalpy

nucleophilic substitutions and eliminations generally only occur on

sp³ hybridized carbons

Sub and Elim reaction tend to favor the direction in which the leaving group is BLANK than the nucleophile

a weaker base

Alkoxides are

good nucleophiles/strong bases

A traditional leaving group bonded to a double carbon bond is

not reactive as a leaving group

Leaving groups on primary carbons are susceptible to displacement in what mechanisms

one-step/bimolecular

Identify the mechanism

Hydrolysis

What does not count as a substituent in determining the degree of substitution on a carbon?

Deuterium

In substitution reactions, a negatively charged nucleophile is

faster in reaction

Low electronegativity of atoms in a nucleophile implies BLANK in subsitution reactions

faster reaction rate

nucleophilic strength BLANK with increasing atomic size when nucleophilic atoms are in the same column of the periodic table in substitution

increases

Less bulky nucleophiles react

faster in substitution

nucleophiles that can be resonance stabilized react

slower in substitution

bulkier substituted nucleophiles will react faster in BLANK reactions

elimination

The optical rotation value of a enantiomer of a compound is the

opposite charge of the original compound (equal magnitude opposite direction)

vinylic halides do NOT normally undergo what mechanisms

substitution

allylic and benzylic alkyl halides undergo what mechanism faster than other halides

Sn2

cleavage of an ether requires what

a strong acid who’s conjugate base is a strong nucleophile

phenols and phenyls do not undergo

Sn1 or Sn2 reactions

what type of ethers are not cleaved by HBr or HI?

diaryl ethers

ring opening of epoxides happens via

Sn2 (whether or not the ring oxygen is protonated)

If the ring oxygen of an epoxide is not protonated the nucleophile attacks the

less substituted carbon atom

If the ring oxygen of an epoxide is protonated the nucleophile attacks the

more highly substituted carbon if it is a tertiary carbon, otherwise the attack occurs at both carbons to give a mixture of products

fused ring epoxides will give a product in which the nucleophile and alcohol groups are

trans

a resonance stabilized alkyl halide (allylic) will undergo Sn1

faster than the other alkyl halides

Secondary and tertiary alcohols react with hydrogen halides via

Sn1

1,2-alkyl or 1,2-hydride rearrangements can occur during reaction between OH and HX when

a more stable carbocation can be formed from the initial carbocation

When elimination occurs in a cyclohexane ring, the hydrogen atom and leaving group are

trans and diaxial

how is this alkene substituted?

monosubstituted

how is this alkene substituted?

disubstituted

how is this alkene substituted?

trisubstituted

how is this alkene substituted?

tetrasubstituted

identify the mechanism

dehydrohalogenation

a nucleophile with low electronegativity will have faster

substitution reactions

a negatively charged nucleophile make substitution reactions

faster

higher bulkiness in a nucleophile leads to BLANK substitution, and lower bulkiness in a nucleophile leads to BLANK susbtitution

slower, faster

the larger the leaving group

the faster the nucleophilic reaction

in order to rearrange atoms to be anti to one another in an alkane

rotate individual carbons

to determine where the alkene forms after E, you must identify the

most acidic hydrogen adjacent to the leaving group carbon

dehydration reactions will commonly use acids such as BLANK, since their conjugate bases are BLANK, leaving elimination as a primary pathway

H₂SO₄ or H₃PO₄, poor nucleophiles

Sn2 is highly sensitive to BLANK in the alkyl substrate

steric hindrance

CH₃OK is a BLANK nucleophile, while CH₃OH is a BLANK nucleophile

strong, weak

Methylamine is more BLANK than methanol

basic

The longer the bond length, the better the

Leaving group

A secondary carbon with a strong base will proceed with

E2 reaction

in an E2 elimination which atom will be attacked by the nucleophile?

The axial atom on the least substituted adjacent carbon to the carbon with the leaving group

From which carbon is the hydrogen removed during dehydrohalogenation?

the most substituted adjacent carbon

Aryl halides will not undergo

substitutions