Chapter 7 Flashcards
triple bonds are … than double bonds, which are … than single bonds.
shorter; shorter
a pi bond in an alkyne is … than a pi bond in an alkene
weaker
if a hydrocarbon contains more than one triple bond, we use the infixes …, .., and so forth
adiyn; atriyn
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
double bond
a hydrogen bonded to a triply bonded carbon of a … alkyne is sufficiently acidic that it can be removed by a strong base
terminal
because water is a stronger acid than acetylene, the hydroxide ion is not a … to convert a terminal alkyne to an alkyne anion
strong enough base
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 …
nucleophile; replaces the halogen atom; nucleophilic substitution
nucleophilic substitution is also called … because an alkyl group is added to a molecule
alkylation reaction
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
middle; internal alkyne; new C-C bonds
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 …
dehydrohalogenations; hydrohalogenation; dehydrohalogenation
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 …
dehydrohalogenation; haloalkene
… 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
2; 3rd; dehydrohalogenation; water or aqueous acid
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
allene; C-C double bonds; C=C=C
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 ..
stereoselective; anti; preference for anti addition
addition of hydrogen halides to an alkyne is … It follows …; H adds to the less substituted C
regioselective; Markovnikov’s rule
vinylic carbocation: a carbocation on a …
doubly bonded C
(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 …
vinylic carbocation
(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 ..
electrophile; nucleophile; vinylic bromoalkene
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
less; sp; sp2
(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 …
the halogen; delocalization; positive charge; resonance
the hydroboration of an internal akyne stops after the addition of … moles of borane. the product is a trialkenylborane
one;
hydroboration of alkynes is …; it involves … addition of H and B
stereoselective; syn
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 …
alkenyl; sterically hindered disubstituted borane
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
regioselective; less substituted
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 …
enol; alkene; alcohol
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 …
C; C-C double bond; C-O double bond
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 …
more; stronger; bond strengths
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
H atom; another atom; double bond;
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
oxymercuration
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 ..
Markovnikov’s addition; ketone
(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
electrophile; bridged mercurinium ion;
(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
nucleophile; electrophile; opposite; more
(HgSO4/H2SO4 Catalyzed Hydration of an Alkyne) Step 3: take a proton away: proton transfer to solvent gives an
organomercury enol
(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 …
carbonyl; oxonium
(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 …
Hg2+; ketone
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 …
two moles; alkane
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
Lindlar’s catalyst; syn
alkynes can alsob e reduced to alkenes by using either … or … metal in … or in low molecular weight primary or secondary amines
sodium; lithium; liquid ammonia
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
stereoselective; anti addition
(Reduction of an Alkyne by Na in Liquid NH3)
Step 1: a one-electron reduction of the alkyne gives an …
alkenyl radical anion
(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 ..
ammonia; alkenyl radical
(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
alkenyl anion
(Reduction of an Alkyne by Na in Liquid NH3) step 4: a second proton-transfer reaction completes the reduction and gives the
trans-alkene
