Chapter 8

Question 1

compounds of the type CHX3 are called

Answer 1

haloforms

Question 2

C-X bonds with halogens are … with a partial… on halogen and a … on C

Answer 2

polarized; negative charge; partial positive charge

Question 3

constitutional isomers with branched chains have … boiling points than their unbranched-chain isomers

Answer 3

lower

Question 4

for an alkane and haloalkane of comparable size and shape, the … has a higher bp. this is due to the … and greater …

Answer 4

haloalkane; dipole moment; polarizability

Question 5

the bps of fluoroalkanes are comparable to those of hydrocarbons of similar molecular weight. this is attributable to the … of F, its high …, and particularly low …

Answer 5

small size; electronegativity; polarizability

Question 6

all liquid bromo and iodoalkanes are … than that of water

Answer 6

greater

Question 7

with the exception of C-F bonds, C-X bonds are … than C-H bonds as measured by bond dissociation enthalpies, which are a measure of bond strengths

Answer 7

weaker

Question 8

radicals are chemical species that contain one or more …

Answer 8

unpaired electrons

Question 9

radicals are produced from a molecule by … of a bond in such a way that each atom/fragment participating in the bond retains …, a process called …

Answer 9

cleavage; one electron; hemolytic bond cleavage

Question 10

as the size of the halogen atom increases, the C-X bond length … and its strength …

Answer 10

increases; decreases

Question 11

halogenation of alkanes occurs via a … reaction. Monosubstituted products are only obtained using an …

Answer 11

substitution; excess of alkane

Question 12

for hydrobromination of alkanes, the rxn is highly …

Answer 12

regioselective

Question 13

Both Br and Cl are regioselective in H replacement in the order …, regioselectivity is far greater for Br than for Cl

Answer 13

3 > 2 > 2

Question 14

in general, interactions that are stabilizing to … are also stabilizing to radicals

Answer 14

carbocations

Question 15

halogenation of alkanes occur by a type of mechanism called a

Answer 15

radical chian mechanism

Question 16

a radical chain mechanism involves three types of steps:

1. …
2. …
3. ..

Answer 16

chain initiation; chain propagation; chain termination

Question 17

chain initiation involves formation of … from …

Answer 17

radicals; nonradicals

Question 18

chain propagation involves reaction of a … and a … to form a …

Answer 18

radical; molecule; new radical

Question 19

chain termination involves … of radicals. there are two types of terminations: … and …

Answer 19

destruction; coupling; disproportionation

Question 20

disproportionation involves transfer of a H from the … position of one radical to another radical and formation of an … and an …

Answer 20

beta; alkane; alkene

Question 21

the number of times a cycle of chain propagation steps repeats is called …

Answer 21

chain length

Question 22

Hammond’s postulate: the structure of the transition state for an exothermic rxn step is reached relatively … in the rxn, so it resembles the … of that step more than the … Conversely, the structure of the transition state for an endothermic rxn step is reached relatively …, so it resembles the … of that step more than the ..

Answer 22

early; reactants; products; late; products; reactants

Question 23

changes in starting material energy affect the transition state of an … rxn more than changes in product energy. The converse is true for an .. rxn

Answer 23

exothermic; endothermic

Question 24

the rate-determining step for the radical halogenation of alkanes is the … by a halogen radical

Answer 24

abstraction of a H

Question 25

abstraction of H by Cl2 is ..., which means that the TS is reached early in the course of the rxn. Therefore, it resembles the ..., so there is little ... character on C in this TS, and regioselectively in radical Cl is only slightly influenced by relative stabilities of radical intermediates

Answer 25

exothermic; reactants; radical

Question 26

reaction between an alkene and NBC involves a ...: a bromine in NBS and a H in the alkene exchange places

Answer 26

net double substitution

Question 27

allylic bromination and chlorination proceed by a ... as well

Answer 27

radical chain mechanism

Question 28

an allyl radical is even more stable than a

Answer 28

tertiary alkyl radical

Question 29

the conjugated system of the allyl radical involves the formation of ... MOS by ...

Answer 29

3; overlap of 3 2p orbitals

Question 30

in the ground state of the allyl radical, 2 e- of the pi system lie in the pi bonding MO and the third lies in the pi nonbonding MO; the antibonding MO is unoccupied. because the lowest pi MO is at a lower energy than the isolated 2p atomic atoms, putting two eelectrons in this MO releases .., which accounts for the stability of the allyl radical

Answer 30

considerable energy

Question 31

the rxn will occur to generate the alkene product that is more stable: in other words, with the more

Answer 31

highly substituted double bond

Question 32

(radical initiated non-markovnikov addition of HBR to alkenes) chain initiation: hemolytic cleavage of a dialkyl peroxide is induced by ... or ... to give two ... radicals, one of which reacts with HBR by ... to give an ... and a ..

Answer 32

light; heat; alkoxy radicals; hydrogen abstraction; alcohol; bromine radical

Question 33

(radical initiated non-markovnikov addition of HBR to alkenes) chain propagation: a bromine radical adds to the C-C double bond regioselectively to give the ... C radical, which reacts with a a molecule of HBr to give the ... and to generate a new ...

Answer 33

more substituted; bromoalkene; bromine radical

Question 34

(radical initiated non-markovnikov addition of HBR to alkenes) chain termination: combination of a ... and a ... and the combination of two ...

Answer 34

carbon radical; bromine radical; bromine radicals

Question 35

(radical initiated non-markovnikov addition of HBR to alkenes) the observed non-Mark regioselectivity of radical addition of HBr to an alkene is a combination of a ... factor and an ... factor

Answer 35

steric; electronic

Question 36

the regiochemistry of polar and radical mechanisms are dominated by the rxns that proceed through the most stable

Answer 36

reactive intermediates

Question 37

non-Mark addition occurs only with

Answer 37

HBr