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Chapter 8 Flashcards

1
Q

compounds of the type CHX3 are called

A

haloforms

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2
Q

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

A

polarized; negative charge; partial positive charge

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3
Q

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

A

lower

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4
Q

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

A

haloalkane; dipole moment; polarizability

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5
Q

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 …

A

small size; electronegativity; polarizability

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6
Q

all liquid bromo and iodoalkanes are … than that of water

A

greater

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7
Q

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

A

weaker

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8
Q

radicals are chemical species that contain one or more …

A

unpaired electrons

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9
Q

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 …

A

cleavage; one electron; hemolytic bond cleavage

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10
Q

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

A

increases; decreases

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11
Q

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

A

substitution; excess of alkane

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12
Q

for hydrobromination of alkanes, the rxn is highly …

A

regioselective

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13
Q

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

A

3 > 2 > 2

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14
Q

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

A

carbocations

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15
Q

halogenation of alkanes occur by a type of mechanism called a

A

radical chian mechanism

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16
Q

a radical chain mechanism involves three types of steps:

  1. …
  2. …
  3. ..
A

chain initiation; chain propagation; chain termination

17
Q

chain initiation involves formation of … from …

A

radicals; nonradicals

18
Q

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

A

radical; molecule; new radical

19
Q

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

A

destruction; coupling; disproportionation

20
Q

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

A

beta; alkane; alkene

21
Q

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

A

chain length

22
Q

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 ..

A

early; reactants; products; late; products; reactants

23
Q

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

A

exothermic; endothermic

24
Q

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

A

abstraction of a H

25
Q

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

A

exothermic; reactants; radical

26
Q

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

A

net double substitution

27
Q

allylic bromination and chlorination proceed by a … as well

A

radical chain mechanism

28
Q

an allyl radical is even more stable than a

A

tertiary alkyl radical

29
Q

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

A

3; overlap of 3 2p orbitals

30
Q

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

A

considerable energy

31
Q

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

A

highly substituted double bond

32
Q

(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 ..

A

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

33
Q

(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 …

A

more substituted; bromoalkene; bromine radical

34
Q

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

A

carbon radical; bromine radical; bromine radicals

35
Q

(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

A

steric; electronic

36
Q

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

A

reactive intermediates

37
Q

non-Mark addition occurs only with

A

HBr

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