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Chapter 7 Flashcards

1
Q

triple bonds are … than double bonds, which are … than single bonds.

A

shorter; shorter

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2
Q

a pi bond in an alkyne is … than a pi bond in an alkene

A

weaker

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3
Q

if a hydrocarbon contains more than one triple bond, we use the infixes …, .., and so forth

A

adiyn; atriyn

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4
Q

when a C-C double bond and a C-C triple bond are both present in the same molecule, the IUPAC rules specify that the location of the … takes precedence in numbering the compound

A

double bond

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5
Q

a hydrogen bonded to a triply bonded carbon of a … alkyne is sufficiently acidic that it can be removed by a strong base

A

terminal

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6
Q

because water is a stronger acid than acetylene, the hydroxide ion is not a … to convert a terminal alkyne to an alkyne anion

A

strong enough base

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7
Q

an acetylide ion is a …; it has an unshared pair of electrons that it can donate to another atom to form a new covalent bond. in this instance, an acetylide anion donates its unshared pair of electrons to the carbon of a methyl or primary haloalkane, and in so doing, the acetylide nucleophile … This type of reaction is called a …

A

nucleophile; replaces the halogen atom; nucleophilic substitution

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8
Q

nucleophilic substitution is also called … because an alkyl group is added to a molecule

A

alkylation reaction

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9
Q

the process of alkylation can be repeated, and a terminal alkyne can, in turn, be converted to an alkyne with the C-C triple bond in the … of a carbon chain. Such an alkyne is usually referred to as an … An important feature of this reaction is that … are made, allowing the construction of larger C backbones from smaller ones

A

middle; internal alkyne; new C-C bonds

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10
Q

treating the dihaloalkane with two moles of a strong base such as sodium amide in liquid ammonia brings about two successive … Recall that addition of HX to an alkene is called …; removal of HX from a haloalkane is called …

A

dehydrohalogenations; hydrohalogenation; dehydrohalogenation

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11
Q

with weaker bases such as sodium hydroxide or potassium hydroxide in ethanol, it is often possible to stop the reaction after the first … and isolate the …

A

dehydrohalogenation; haloalkene

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12
Q

… moles of sodium amide are required for the double dehydrohalogenation reaction. However, for terminal alkynes, the alkyne formed reacts with sodium amide to give an alkyne salt. Therefore, a … mole of sodium amide is required to complete the … of the remaining bromoalkene. Addition of … completes the sequence

A

2; 3rd; dehydrohalogenation; water or aqueous acid

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13
Q

in dehydrohalogenation of a haloalkene with at least one H on each adjacent carbon, a side reaction occurs, namely the formation of an …, which has two adjacent …, that is, it contains a … function group

A

allene; C-C double bonds; C=C=C

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14
Q

Addition of bromine to a triple bond is …, The major product corresponds to … addition of the two bromine atoms. carrying out the bromination in acetic acid with added bromide ion significantly increases the ..

A

stereoselective; anti; preference for anti addition

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15
Q

addition of hydrogen halides to an alkyne is … It follows …; H adds to the less substituted C

A

regioselective; Markovnikov’s rule

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16
Q

vinylic carbocation: a carbocation on a …

A

doubly bonded C

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17
Q

(addition of HBr to an alkyne)
Step 1: make a new bond between a nucleophile and an electrophile–add a proton: proton transfer from HBr to the alkyne gives a …

A

vinylic carbocation

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18
Q

(addition of HBr to an alkyne)
step 2: make a new bond between a nucleophile and an electrophile: reaction of the vinylic carbocation (a …) with bromide ion (a …) gives the ..

A

electrophile; nucleophile; vinylic bromoalkene

19
Q

alkynes are considerably … reactive toward most electrophilic additions than are alkenes, primarily due to the instability of the … hybridized vinylic carbocation intermediate formed from an alkyne compared with the … hybridized alkyl carbocation formed from an alkene

A

less; sp; sp2

20
Q

(addition of HBr to an alkyne) for addition of a second mole, the electron pair of the remaining pi bond reacts with HBr to form a carbocation. of the two possible carbocations, the one with the positive charge on the carbon bearing … is favored because of … of the … through …

A

the halogen; delocalization; positive charge; resonance

21
Q

the hydroboration of an internal akyne stops after the addition of … moles of borane. the product is a trialkenylborane

A

one;

22
Q

hydroboration of alkynes is …; it involves … addition of H and B

A

stereoselective; syn

23
Q

terminal alkynes also react regioselectively with borane to form trialkenylboranes. in practice, however, the reaction is difficult to stop at this stage because the … group reacts further with borane to undergo a second hydroboration. It is possible to prevent the second hydroboration step, and, in effect, stop the rxn at the alkenylborane stage by using a …

A

alkenyl; sterically hindered disubstituted borane

24
Q

as with hydroboration of unsymmetrical alkenes, the addition of (sia)2BH to a C-C triple bond of a terminal alkene is …; boron adds to the … C

A

regioselective; less substituted

25
Q

the initial product of hydroboration-oxidation of an alkyne is an …, a compound containing a hydroxyl group bonded to a C of a C-C double bond. the name enol is derived from the fact that it is both an … and an …

A

enol; alkene; alcohol

26
Q

enols are in equilibrium with a constitutional isomer formed by migration of a H atom from oxygen to … and rearrangement of the … to form a …

A

C; C-C double bond; C-O double bond

27
Q

keto forms in general are … stable than enol forms because a C=O pi bond is generally …. than a C=C pi bond, whereas C-H and O-H pi bonds generally have similar …

A

more; stronger; bond strengths

28
Q

tautomers are constitutional isomers that are in equilibrium with each other and differ only in the location of a … or … and a … relative to a heteroatom (atom that isn’t C or H-, most commonly O, N, or S

A

H atom; another atom; double bond;

29
Q

in the presence of concentrated sulfuric acid and Hg(II) salts as catalysts, alkynes undergo the addition of water in a reaction analogous to the … of alkenes. The Hg(II) salts most often used for this purpose are HgO, HgSO4, or Hg(OAc)2

A

oxymercuration

30
Q

for terminal alkynes, addition of water follows …; hydrogen adds to the C of the triple bond bearing the H. The resulting enol is in equilibrium with the more stable keto more, so the product isolated is a ..

A

Markovnikov’s addition; ketone

31
Q

(HgSO4/H2SO4 Catalyzed Hydration of an Alkyne)
step 1: make a new bond between a nucleophile and an electrophile: attack of the C-C triple bond on the Hg2+ (an …) gives a … intermediate

A

electrophile; bridged mercurinium ion;

32
Q

(HgSO4/H2SO4 Catalyzed Hydration of an Alkyne) Step 2: make a new bond between a nucleophile and an electrophile: attack of water (a …) on the bridged mercurinium ion intermediate (an …) from the side … the bridge opens the three membered ring. Because the secondary vinylic cation makes a greater contribution than the primary, attack of water occurs preferentially at the … substituted C

A

nucleophile; electrophile; opposite; more

33
Q

(HgSO4/H2SO4 Catalyzed Hydration of an Alkyne) Step 3: take a proton away: proton transfer to solvent gives an

A

organomercury enol

34
Q

(HgSO4/H2SO4 Catalyzed Hydration of an Alkyne) step 4: keto-enol tautomerism
Step 5: add a proton: proton transfer to the … of the keton gives an …

A

carbonyl; oxonium

35
Q

(HgSO4/H2SO4 Catalyzed Hydration of an Alkyne) steps 6 and 7: break a bond to give stable molecules/ions followed by keto-enol tautomerism: loss of … from the oxonium ion gives the enol form of the final product. Tautomerism of the enol gives the …

A

Hg2+; ketone

36
Q

treatment of an alkyne with H2 in the presence of a transition metal catalyst results in the addition of … of H2 to the alkyne and its conversion to an …

A

two moles; alkane

37
Q

it’s possible to stop reduction of an alkyne after addition of one mole of H. the catalyst most commonly used for this is known as …–a stereoselective catalyst that leads to … addition of two H atoms tot the C-C triple bond

A

Lindlar’s catalyst; syn

38
Q

alkynes can alsob e reduced to alkenes by using either … or … metal in … or in low molecular weight primary or secondary amines

A

sodium; lithium; liquid ammonia

39
Q

reduction of an alkyne to an alkene by Li or NA in NH3(l) is …; in involves mainly … addition of two Hs to the triple bond

A

stereoselective; anti addition

40
Q

(Reduction of an Alkyne by Na in Liquid NH3)

Step 1: a one-electron reduction of the alkyne gives an …

A

alkenyl radical anion

41
Q

(Reduction of an Alkyne by Na in Liquid NH3) step 2: add a proton- the alkenyl radical anion (a very strong base) abstracts a proton from a molecule of … to give an ..

A

ammonia; alkenyl radical

42
Q

(Reduction of an Alkyne by Na in Liquid NH3) Step 3: a one-electron reduction of the alkenyl radical gives an … The trans-alkenyl anion is more stable than its cis isomer, and the stereochemistry of the final product is determined in this step

A

alkenyl anion

43
Q

(Reduction of an Alkyne by Na in Liquid NH3) step 4: a second proton-transfer reaction completes the reduction and gives the

A

trans-alkene

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