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Chapter 6 Flashcards

1
Q

the most characteristic reaction of alkenes is … to the C-C double bond in such a way that the pi bond is …, and, in its place, … bonds form to two new atoms or groups of atoms

A

addition; broken; sigma bonds form;

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2
Q

another addition reaction of alkenes is a formation of … in the presence of certain catalysts called …, many alkenes form polymers made by the addition of … to a growing …

A

chain-growth polymers; initiators; monomers; polymer chain

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3
Q

in a reaction that occurs in two or more steps, each step has its own … and …

A

transition state; activation energy

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4
Q

a reactive intermediate corresponds to an … between two transition states

A

reactive intermediate

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5
Q

because the energies of the intermediates are higher than that of either reactants or products, they are highly … and usually cannot be …

A

reactive; isolated

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6
Q

the slowest step in a multistep reaction, called the …, is the step that crosses the …

A

rate-determining step; highest energy barrier

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7
Q

each step of a chemical reaction involves the crossing of a peak on an energy diagram. the peaks represent chemical structures on the energy ssurfaces that are … between …

A

transitions; stable structures

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8
Q

reaction intermediates are represented in wells (troughs) on the energy surfaces. the peaks on the surface are referred to as

A

transition states

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9
Q

reaction intermediates have lifetimes … than the time it takes for a bond to vibrate, whereas transition states have lifetimes only on the order of the … of a bond vibration. The chemical structures of transition states can be considered as having no …

A

longer; lifetime; measurable lifetime

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10
Q

equilibrium in a chemical reaction usually favors the side with stronger

A

chemical bonds

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11
Q

bond strengths are reported as …, defined as the energy needed to … any bond

A

bond dissociation enthalpies; break

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12
Q

the overall reaction of electrophilic species adding to pi bonds is called .. The key step in these mechanisms involves the pi electrons of the alkene reacting as a … or … with an … species

A

electrophillic addition; nucleophile; Bronsted-Lowry base; electrophilic

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13
Q

three features can make a molecule or an ion electrophilic:

  • a region of low …, reflected by a … or .. charge. This aids reaction with an electron rich region of a nucleophile through …
  • the lack of an … on an atom
  • a relatively … to an atom that can depart as a … or … These can be considered electron-seeking because their reactions with nucleophiles create … and therefore more … molecules
A

electron density; partial; full positive; electrostatic attraction; octet; weak bond; stable ion; molecule; stronger bonds; stable

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14
Q

the hydrogen halides HCl, HBr, and HI add to alkenes to give … These additions may be carried out either with the pure reagents or in the presence of a … such as acetic acid

A

haloalkenes; polar solvent

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15
Q

a regioselective reaction is a reaction in which one direction of … or … occurs in preference to all others

A

bond forming; breaking

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16
Q

Regioselectivity was noted by Vladimir Markovnikov who made the generalization known as Markovnikov’s rule: in the addition of H–X to an alkene, hydrogen adds to the double-bonded carbon that has the …

A

greater number of hydrogens already bonded to it

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17
Q

electrophilic addition steps:

  • add a ..
  • make a new bond between a … and an …
A

proton; nucleophile; electrophile

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18
Q

the pi bond is relatively electron-rich because the pi bonding electron density is … and … the bond axis, not between the positively charged atomic nuclei as is the case with sigma bonding e- density –> more …

A

above; below; delocalization

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19
Q

Step 1 in proton addition rxns (the addition of a proton to the alkene) results in formation of a … called a …

A

cationic intermediate; carbocation

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20
Q

all carbocations are … as well as …

A

electrophiles; Lewis acids

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21
Q

the carbocation has an

A

empty p orbital

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22
Q

the physical structure of the transition state is the … that gives way to the carbocation intermediate

A

lowest-energy contorted geometry

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23
Q

the second step of the proton addition rxn is much easier than the first because the reactant is now a …, which is a highly reactive electrophile due to their … and the lack of an … at C

A

carbocation; positive charge; octet

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24
Q

because the highly electrophilic cation intermediate is so unstable, the energy necessary in the collision to surmount the second barrier is

A

very low

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25
Q

Reaction of HX and an alkene can, at least in principle, give two different carbocation intermediates because the proton could be transferred to either of the doubly bonded C atoms. We know, though, that a … carbocation is more stable and requires a lower Ea for its formation than a …, and a … carbocation is more stable and requires a lower Ea for its formation than a … carbocation. A more stable carbocation intermediate forms … than a less stable carbocation intermediate

A

tertiary; secondary; secondary; primary; faster

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26
Q

Alkyl groups stablize carbocations through …, which involves partial … of the sigma bonding orbital of an adjacent C-H or C-C bond of the alkyl group with the … of the cationic C. In other words, some e- density of the alkyl group C-H or C-C bond is mixed into the ..

A

hyperconjugation; overlapping; vacant 2p orbital; 2p orbital

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27
Q

the net result of hyperconjugation is an increase of … on the cationic carbon, thereby … the positive charge onto the adjacent alkyl groups. As more alkyl groups are bonded to a cationic carbon, the hyperconjugation effect becomes … and the carbocation becomes more …

A

electron density; delocalizing; stronger; stable

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28
Q

in the presence of an acid catalyst, most commonly concentrated sulfuric acid, water adds to an alkene to give an … The addition of water is called ..

A

alcohol; hydration

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29
Q

in the case of simple alkenes, H adds to the carbon of the double bond according to … and OH adds to the carbon with the …

A

Markovnikov’s rule; fewer hydrogens

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30
Q

mechanism for acid-catalyzed hydration:

  1. add a … (water reacts with H2SO4 to form …)
  2. make a new bond between a … and an …
  3. take a … away: it is lost to the … in solution, and the product yields a new …
A

proton; hydronium ion; nucleophile; electrophile; proton; water; acid catalyst (H3O+)

31
Q

rearrangement: sometimes, if it creates a more stable structure, either an … or a … migrates, each with its bonding electrons, from an adjacent atom to the … atom

A

alkyl group; hydrogen; electron-deficient atom

32
Q

carbocation rearrangement mechanism

  1. Add a …
  2. …
  3. make a new bond between a … and an …
A

proton; 1, 2 shift; nucleophile; electrophile

33
Q

Cl2 and Br2 react with alkenes at room temp by adding halogen atoms to the two Cs of the double bond. F2 adds to alkenes but because its reactions are very … and …, this reaction is not useful. I2 also adds, but is also …

A

fast; difficult to control; not useful

34
Q

the addition of Br or Cl to a cycloalkene is an example of a … reaction, in which one … is formed in preferred to all others

A

stereoselective; stereoisomer

35
Q

Cl2 and Br2 as reagents add … –> they occur with ..

A

anti; anti stereoselectivity

36
Q

Mechanism for addition of Br2/Cl2 with anti stereoselectivity:

  1. make a new bond between a … and an .. –> rxn is initiated by interaction of the … with … A … or … is formed
  2. make a new bond between a … and an … –> attack of … on … from the side … opens the ring to give the anti product
A

nucleophile; electrophile; pi electrons; bromine/chlorine; bridged bromonium ion or bridged chloronium ion; nucleophile; electrophile; bromide ion; C; opposite the bromonium ion

37
Q

the bromines/chlorines are not only anti but also … Thus, this is an … attack

A

in the same plane (coplanar); anti-coplanar

38
Q

Addition of Cl or Br to cyclohexene and its derivates gives a … product because only … positions on adjacent atoms of a cyclohexane ring are … and …

A

trans diaxial; axial; anti; coplanar

39
Q

treating an alkene with Br2 or Cl2 in the presence of water results in addition of … and …, or … and …, to the C-C double bond to give a …

A

OH; Br; OH; Cl; halohydrin

40
Q

Addition of HOCl and HOBr is … and …

A

regioselective; anti stereoselective

41
Q

Mechanism for halohydrin formation and its anti stereoselectivity:

  1. make a new bond between a … and an …: reaction of the … with … gives a … intermediate
  2. make a new bond between a … and an …: attack of … ( a… ) on the … substituted C of the bridged ion opens the ring.
  3. take a … away
A

nucleophile; electrophile; pi electrons; bromine; bridged bromonium ion; nucleophile; electrophile; H2O; nucleophile; more; proton

42
Q

(for halohydrins) The C-halogen bond to the more substituted carbon of the halonium ion is … than the bond to the less substituted carbon. this difference in lengths means that the ring-opening transition state can be reached more easily by attack at the … C

A

longer; more substituted

43
Q

the result of oxymercuration followed by sodium borohydride reduction is … of … to an alkene

A

Markovnikov addition; H-OH

44
Q

oxymercuration is …: HgOAC becomes bonded to the … of the alkene, and OH of water becomes bonded to the … C

A

regioselective; less substituted C; more substituted

45
Q

Reduction of the organomercury compound by sodium borohydride (NaBH4) replaces HgOAc by …

A

H

46
Q

oxymercuration reduction occurs without because no … is formed

A

rearrangement; free carbocation intermediate

47
Q

mechanism for oxymercuration-reduction of an alkene:

  1. … to give stable molecules/ions: dissociation of mercury(II) acetate gives … (an …) and acetate anion
  2. make a new bond between a … and an …: attack of the … onto … forms a … intermediate (this is not a true …)
  3. make a new bond between a … and an …: anti attack of … on the bridged intermediate occurs at the … C to open the ring
  4. take a … away: transferred to …
  5. reduce the C-HgOAc bond to …
A

break a bond; AcOHg+; electrophile; nucleophile; electrophile; alkene pi bond; AcOHg+; bridged mercurinium ion; carbocation; nucleophile; electrophile; water; more substituted; proton; water; C-H

48
Q

the net reaction from hydroboration and subsequent oxidation of an alkene is …

A

hydration of a C-C double bond

49
Q

the regiochemistry of hydroboration and subsequent oxidation is …

A

non-Markovnikov

50
Q

hydroboration-oxidation occurs without

A

rearrangement

51
Q

hydroboration is the addition of … (..) to an alkene to form a …

A

borane; BH3; trialkylborane

52
Q

Because of the vacant 2p orbital in the valence shell of boron, BH3, and all other trivalent compounds of boron are … They resemble …, but they are …

A

electrophiles; carbocations; electrically neutral

53
Q

addition of borane to alkenes is … and …:
upon addition of borane to an unsymmetrical alkene, boron becomes bonded predominantly to the … C of the double bond (…)
H and B add from … of the double bond; that is, the reaction is … stereoselective

A

regioselective; stereoselective; less substituted; non-Markovnikov; the same face; syn

54
Q

hydroboration mechanism:

  1. lewis acid-base …
  2. make a new bond between a … and … with simultaneous …: the boron adds to the … C, due to … and some … effects
A

coordination; nucleophile; electrophile; bond formation to H; less substituted; steric; electronic

55
Q

… is an oxidizing agenet and oxidizes a trialkylborane to an alcohol and sodium borate

A

hydrogen peroxide

56
Q

oxidation of a trialkylborane by alkaline hydrogen peroxide

  1. make a new bond between a nucleophile and an electrophile: donation of a pair of e- from a … to the … atom of the trialkylborane gives an intermediate in which boron has a … charge
  2. …: rearrangement of an R group to an … results in ejection of … ion (occurs twice)
  3. reaction of the trialkylborate with aqueous NaOH gives the …
A

hydroperoide ion (nucleo); boron (electrophile); negative formal; 1,2 shift; adjacent oxygen; hydroxide; alcohol

57
Q

hydrogen peroxide oxidation of a trialkylborane is … in that the configuration of the alkyl group is retained. The net result of hydroboration-oxidation of an alkene is … stereoselective addition of … and … to a C-C double bond, combined with … regioselectivity

A

stereoselective; syn; H; OH; non-Markovnikov

58
Q

oxidation is the … of electrons and reduction is the … of electrons

A

loss; gain

59
Q

oxidation: the addition of … to and/or removal of … from a C atom

A

O; H;

60
Q

reduction: the removal of … from and/or addition of .. to a C

A

O; H

61
Q

oxidation of an alkene by OsO4 is … stereoselective

A

syn stereoselective

62
Q

oxidation of an alkene by OsO4 involves syn addition of an … group to each C of the double bond

A

OH

63
Q

the syn stereoselectivity of the osmium tetroxide oxidation of an alkene is accounted for by the formation of a cyclic osmate in such a way that the five-membered osmium-containing ring is bonded in a … configuration to the original alkene

A

cis

64
Q

usually, the osmate is treated directly with a …, such as …, which cleaves the osmium-oxygen bonds to give a … and reduced forms of osmium

A

reducing agent; NaHSO3; cis glycol

65
Q

ozonolysis cleaves the C-C double bond and forms two … groups in its place

A

carbonyl C=O

66
Q

O3 is strongly

A

electrophilic

67
Q

ozonolysis is one of the few organic reactions that breaks

A

C-C bonds

68
Q

mechanism for ozonolysis:

  1. ozone reacts with the alkene with both … and … character in a single, simultaneous step
  2. break a bond to give stable molecules/ions: relocating valence e- in the molozonide results in … of one C-C and one O-O bond. the fragments then recombine to form an …
  3. reduction of the ozonide and … results in the final carbonyl fragments
A

electrophilic; nucleophilic character; cleavage; ozonide; cleavage

69
Q

conversion of an alkene to an alkane involves reduction by … in the presence of a …: process is …, or …

A

hydrogen; catalyst; catalytic reduction; catalytic hydrogenation

70
Q

catalytic reduction is …, with the vast majority proceeding by … addition of H to the C-C double bond

A

stereoselective; syn;

71
Q

an optically active compound can never be produced from … starting materials reacting in an … environment

A

achiral; achiral

72
Q

an enantiomerically pure product may be produced from … reagents if the reaction takes place in a … environment

A

achiral; chiral

73
Q

a stereospecific rxn is a special type of stereoselective reaction in which the stereochemistry of the product depends on the …

A

stereochemistry of the starting material

74
Q

in catalytic reductions where a new chiral center is formed, a large enantiomeric excess of one enantiomer may be formed, and the reaction is said to be

A

enantioselective

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