__ are hydrocarbons that contain carbon-carbon triple bonds. They are also called __ because they are derivatives of __, the simplest __.
alkynes x3
acetylenes
acetylene
alkyne
The chemistry of the carbon- carbon triple bond is what? A triple bond gives an alkyne what?
What is it's molecular formula?
How many elements of unsaturation (eu) does it have?
similar to that of the double bond
four fewer hydrogens than the corresponding alkane
CnH2n-2
two
Naming alkynes:
- When additional functional grops are present, the suffixes are combined to produce the compound names of the __, __ and so on.
- The IUPAC rules gives __ a higher priorty than __ or __, so the numbering begins at what?
- What happens if the double bond and triple bond are equidistant from the ends of hte chain?
alkenynes (a double bond and a triple bond)
alkynols (a triple bond and an alcohol)
alcohols
alkenes
alkynes
at the end closer to an alcohol
number the chain so the double bond receives a lower number than the triple bond
The common names of alkynes describe them as what?
Most alkynes can be named as a molecule of __ with one or two __.
derivatives of acetylene
acetylene
alkyl substituents
Many of an alkyne's chemical properties depend on whether there is an __, that is, whether the __ comes at the end of a carbon chain. Such an alkyne is called a __ or a __. If the triple bond is located somewhere other than the end of the carbon chain, the alkyne is called an __ or an __.
acetylenic hydrogen (H-C***C)
triple bond
terminal alkyne
terminal acetylene
internal alkyne
internal acetylene
Alkynes are relatively __ and nearly __ in water. They are quite __ in most organic solvents. Many alkynes have characteristic, mildly offensive __. Ethyne, propyne, and butynes are __ at room temp just liek the corresponding alkanes and alkenes. IN fact, the __ of alkynes are nearly the same as those of alkanes and alkenes with similar C skeletons
nonpolar
insoluble
soluble
odors
gases
BP
__ is a colorless, foul-smelling gas that burns in air with a yellow, sooty flame. WHen the flame is supplied with pure oxygen, the color turns to __, and the flame temp increases dramatically.
acetylene
blue
Each carbon atom is bonded to two other atoms, and there are no __. Each carbon atoms needs __ to form the __. Hybridization of the __ wwith one __ gives two hybrid orbitals, directed __ degrees apart, for each carbon atom. Overlap of these __ with each other and with the __ gives the __ framework.
nonbonding valence electrons
two hybrid orbitals
sigma bond framework
s orbital
p orbital
180
sp hybrid orbitals
hydrogen s orbitals
sigma bond
Two __ result from overlap of the two remaining unhybridized __ on each carbon atom. These orbitals overlap at __ to each other, forming one __ with __ above and below the C-C sigma bond, and the other with __ in front and in back of the sigma bond. The shape of these __ is such that they blend to form a __ of __ encircling the sigma bond between the two carbon atoms
pi bonds
p orbitals
right angles
pi bond
electron density
electron density
pi bonds
cylinder of electron density
Triple bonds are (shorter/ longer) than double and single bonds.
The triple bond is relatively __ because of the attractive overlap of __ and the high __ of the sp hybrid orbital. The sp hybrid orbitals are about 1/2 __, using more of the clsoer, hightly held s orbital. The sp hybrid orbitals also account for the slightly __ C-H bonds in acetylene compared with ethylene.
shorter
shorter
three bonding pairs of electrons
s character
s character
shorter
__ are much more acidic than other hydrocarbons. Removal of an __ proton forms an __, which plays a central role in alkyne chemistry.
The acidity of an __ stems from the nature of the __.
What is the trend of acidity?
terminal alkynes
acetylenic proton
acetylide ion
acetylenic hydrogen
sp hybrid triple bond C-H bond
increases with increasing s character of the orbitals: xp3<sp2<sp
True or False:
The vinyl proton is about 10^19 times more acidic than the acetylenic proton.
False
The acetylenic proton is about 10^19 times more acidic than the vinyl proton
Abstraction of an __ gives a __ that has the lone pair of electrons in the sp hybrid orbital. ELectrons in this orbital are __, and there is less __ than in __ with the lone pair in sp2 or sp3 hybrid orbitals.
acetylenic proton
carbanion
close to the nucleus
charge separation
carbanions
Very strong bases deprotonate __ to form __ called __ Hydroxide ioin and alkoxide ions are not strong enough bases to __. __ do not have __, so they do not react
terminal acetylenes
carbanions
caetylide ions (alkynide ions)
deprotonate alkynes
internal alkynes
acetylenic protons
__ is frequently used as the base in forming __. The __ is the conjugate base of ammonia, a compound that is itself a base. __ is also a very weak acid, however, with a pKa=35. One of its hydrogens can be reduced by __ to ogive the sodium salt of the __, a very strong conjugate base.
sodium amide
acetylide salts
amide ion
ammonia
sodium metal
amide ion
__ are strong nucleophiles. Inf act, one of the best methods for synthesizing substituted alkynes is a __ by an __ on an unhindered alkyl halide.
acetylide ions
nucleophilic atack
acetylide ion
What is the first of the two approaches for synthesis of alkynes?
1) an appropriate electrophile undergoes nucleophilc attack by an acetylide ion; the electron may be an unhibdered primary alkyl halide (Sn2) or it can be a carbonyl compound (addition to form an --OH), either of which joins two fragments to give a product with a lengthened carbon skeleton
What is the second of the two approaches for synthesis of alkynes?
2) forms a triple bond by a double dehydrohalogenation of a dihalide; does not enlarge the carbon skeleton; isomerization of the triple bond may occur
An acetylide ion is a __ and a __. What can it do?
strong base
powerful nucleophile
displace a halide ion from a suitable substrate, giving a substituted acetylene
If this Sn2 reaction is to produce a good yield, the alkyl halide must be an __. .It must be __ or __, with no __ or __ close to the reaction center.
excellent Sn2 substrate
methyl or primary
bulky substituents
branches
If the back-side approach is hindered, what happens?
the acetylide ion may abstarct a proton, giving elimination by the E2 mechanism
Like other carbanions, acetylide ions are strong __ and strong __. In addition to displacing halide ions in __, they can add to __. Because oxygen is more electronegative than carbon, the __ is __.
nucleophiles
bases
Sn2 reactions
carbonyl groups
C=O
polarized
The positively charged carbon is __; attack by a __ places a negative charge on the electronegative oxygen atom.
The product of this __ attack is an __, a strong base. (An __ is the conjugate base of an alcohol, a weak acid.) Addition of water or a dilute acid protonates the __ to give the alcohol.
electrophilic
nucleophile
nucleophilic
alkoxide ion x3
An __ can serve as the nucleophile in this addition to a __. The __ adds to the __ to form the __. Addition of dilute acid in a separate step protonates the __ to give the __
acetylide ion
carbonyl group
acetylide ion
carbonyl group
alkoxide ion
alkoxide ion
alcohol
An __ adds to formaldehyde to give (after the protonation step) a __ with one more carbon atom than there was in the __.
An __ adds to an aldehyde to give, after protonation, a __. The two groups of the __ are the __ and the __ that was bonded to the carbonyl group of the aldehyde.
acetylide
primary alcohol
acetylide
acetylide
secondary alcohol x2
acetylide
alkyl group
A __ has two alkyl groups bonded to its carbonyl carbon atom. Addition of an __, followed by protonation, gives a __. The three groups bonded to the __ (the carbon bearing the OH group) are the __ and the two __ originally bonded to the carbonyl group in the ketone.`
