Ch.7-8

Question 1

which carbocations have the most stability

Answer 1

3>2>1>methyl

Question 2

what are some examples of weak bases that are good nucleophiles?

Answer 2

Cl, I, Br, CN, acetate ion

Question 3

why do rearrangements occur

Answer 3

they occur due to carbocations and are driven by the formation of a more stable carbonation

Question 4

why are tertiary carbocations more stable than others?

Answer 4

they have a stronger inductive effect due to

Question 5

What is a 1,2 methyl shift

Answer 5

it is when a methyl group on an adjacent carbon (2 bonds away) shifts to form a more stable carbonation

Question 6

what type of mechanism will occur with an acid catalyzed dehydration on a tertiary alkyl halide?

Answer 6

an E1 mechanism

Question 7

in a 1,2 methyl shift, what is moving?

Answer 7

the electrons in the bond connecting the methyl and the carbon are moving towards the positively charged carbonation, the methyl atoms only move as a result of this electron movement

Question 8

in an acid catalyzed dehydration reaction, what drives the reaction towards a major product?

Answer 8

the formation of the major product is driven by carbonation stability

Question 9

what is the major product in an alkene formation?

Answer 9

the more stable one, it has lower energy and is thermodynamically favorable to form

Question 10

how often do rearrangements occur

Answer 10

rearrangements occur very frequently, if there is the possibility for a more stable carbonation, a methyl or hydride shift will occur

Question 11

what is a 1,2 hydride shift

Answer 11

it is when a hydrogen 2 bonds away from a less stable carbonation shifts towards the positive charge and leads to the formation of a more stable carbonation

Question 12

how are alkynes formed?

Answer 12

through elimination

Question 13

what is a gem-dihalide

Answer 13

it is where you have two halogens that are two bonds away from each other (bonded on same carbon)

Question 14

if you have a gem-dihalide and excess base, what can occur?

Answer 14

you can get the formation of an alkyne through a double dehalogenation

Question 15

what is a vicinal dihalide

Answer 15

it is a compound that bears two halogens on adjacent carbons (3 bonds away)

Question 16

What is sodium amide

Answer 16

it is a strong base

Question 17

what is double dehydrohalogenation

Answer 17

it is a mechanism of a double E2 that forms an alkyne with either a vicinal dihalide or a geminal dihalide

Question 18

what is an important property of terminal alkynes

Answer 18

they are acidic and can be deprotonated to form a nucleophile that can be used in further mechanisms

Question 19

what is an alkylation

Answer 19

it is the formation of a new carbon carbon bond

Question 20

what is the pka of sp, sp2, sp3 and what types of bonds do they represent

Answer 20

sp represents a triple bonded carbon atom and has a pka of 25

sp2 is a double bonded carbon atom that has a pka of 44

sp3 is a single bonded carbon atom that has a pka of 50

Question 21

to deprotonate a terminal alkyne, what type of reagent do we need?

Answer 21

a strong base like NH2

Question 22

after deprotonating a terminal alkyne, what is formed?

Answer 22

an electron rich carbanion that can act as a nucleophile in a substitution reaction

Question 23

what kind of alkyl halide is necessary for a carbanion alkyne to act as a nucleophile

Answer 23

it must be either a primary alkyl halide or a methyl alkylhalide, tertiary and secondary do not work due to the steric effect

Question 24

if you react a carbanion alkyne with a tertiary or secondary akyl halide, what will occur and what will not occur

Answer 24

we would have an E2 reaction, there would be no new carbon-carbon bond formed (alkylation)