Chapter 5

Question 0

allylic carbon

Answer 0

a carbon attached to a vinylic carbon

H2C=CHCH2-

Question 1

vinylic carbon

Answer 1

a carbon that is attached by a double bond

H2C=CH-

Question 2

alkene

Answer 2

hydrocarbons that contain a carbon-carbon double bond

Question 3

alkene nomenclature

Answer 3

H2C=CH2 (ethene or ethylene)

CH3CH=CH2 (propene or propylene)

Question 4

C-C double bonds

Answer 4

take precedence over alkyl groups and halogens in determining the main carbon chain

Question 5

hydroxyl groups (OH)

Answer 5

have precedence over double bond

Question 6

isomers of alkenes

Answer 6

-there is no rotation in C=C (double bonds) because of pi bonding

Question 7

p orbitals

Answer 7

-carbon uses these orbitals in pi bonding

Question 8

cis and trans

Answer 8

-in order to have cis and trans, carbons cannot have the same subgroups on one carbon

Question 9

Z configuration

Answer 9

higher ranked substituents are on the same side (either top or bottom of c=c)

Question 10

E configuration

Answer 10

higher ranked substituents are on opposite sides of the c=c

Question 11

Z and E configuration

Answer 11

are determined by assigning priorities based on atomic number

Question 12

Priority rules

Rule #1

Answer 12

higher atomic number takes precedence over lower

Question 13

Priority rules

Rule #2

Answer 13

when two atoms directly attach to the same carbon of the double bond are identical, compare the atoms attached to these two on the basis of their atomic numbers. Precedence is determined at the first point of difference

Question 14

Priority Rules

Rule #3

Answer 14

work outward from the point of attachment, comparing all the atoms attached to a particular atom before proceeding further along the chain

Question 15

Priority rules
#4

Answer 15

when working outward from the point of attachment, always evaluate substituent atoms one by one, never as a group

Question 16

Priority rules
#5

Answer 16

an atom that is multiply bonded to another atom is considered to be replicated as a substituent on that atom

Question 17

increasing stability of alkenes

Answer 17

in general, alkenes with more highly substituted double bonds are more stable than isomers with less substituted double bonds
-van der waals strain plays are role for cis and trans isomers (trans more stable)

Question 18

degrees of substitution

Answer 18

• monosubstituted: CH3CH2CH=CH2
• disubstituted: CH3CH=CHCH3
• trisubstitued: (CH3)2C=CHCH2CH3
• tetrasubstituted

Question 19

alkyl groups

Answer 19

are better electron releasing substituents than hydrogen and are better able to stabilize an alkene

Question 20

dehydration of alcohols

Answer 20

• the H and OH are lost from adjacent carbons
• acid catalyst is necessary
• converting alcohols to alkenes with H2SO4 (sulfuric acid)

Question 21

which beta carbon does the H come of of in alcohol dehydration

Answer 21

the carbon with less hydrogens

-Zaitsev’s rule

Question 22

beta elimination

Answer 22

• carbon with less hydrogens undergoes elimination

- most stable alkene

Question 23

sterioselective reaction

Answer 23

a single starting material can yield two or more stereoisometric products

Question 24

E1 and E2 mechanisms

Answer 24

• both reactions are promoted by acids

- the relative reactivity increases: primary<tertiary

Question 25

E2 elimination

Answer 25

primary carbocation does not exist–>all steps happen at the same time

Question 26

E1 elimination

Answer 26

secondary and tertiary alcohols

Question 27

why do carbocations rearrange

Answer 27

tertiary carbocations are more stable than secondary carbocations

Question 28

dehydrohalogenation

Answer 28

• the loss of a hydrogen and a halogen from an alkyl halide
• best method of making alkene
• uses a strong base

Question 29

dehydrohalogentation of cycloalkyl halides

Answer 29

leads exclusively to cis cycloalkenes when the ring has fewer than 10 carbons

Question 30

sodium ethoxide

Answer 30

• very strong base
• used in dehydrohalogenation
• made from Na + H-O-CH2CH3

Question 31

rate of dehydrohalogenation

Answer 31

increasing rate: F<br></br><i>slowest rate</i>

I–>fastest rate

Question 32

Dehydrohalogenation

Answer 32

both the alkyl halide and the base are involved in the rate determining step

Question 33

E2 mechanism

Answer 33

has no carbocation formation; therefore, it is the better mechanism to form alkenes

Question 34

dehydrohalogenation

Answer 34

in order for the H and X to be eliminated, they must be in the anti position

Question 35

E2 mechanism of dehydrohalogenation of alkyl halides

Answer 35

key elements

1. base-H bond making
2. C-H bond breaking
3. C=C pi bond formation
4. C-halide breaking (weaker the bond, faster the reaction)

Question 36

E1 mechanism of dehydrohalogenation

Answer 36

• base is missing
• alcohol is the solvent
• rate depends on what type of halide is there
  
  • tertiary halide is the fastest