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5 Summary of Organic Nomenclature -- Part 16
Two different approaches are used for the synthesis of alkynes.
A carbonyl compound or an unhindered primary alkyl halide may be what the electrophile is.
Either reaction joins two fragments and gives a product with a long carbon skeleton.
This approach is used in many laboratories.
The triple bond is formed by a double dehydrohalogenation of a dihalide.
The reaction doesn't enlarge the carbon skeleton.
Dehydrohalogenation is only useful when the product has the triple bond in a favored position.
A strong base and a powerful nucleophile can be found in an acetylide ion.
It can give a substitution for a halide ion.
It is an excellent way to shorten a'X must be a primary alkyl halide) carbon chain.
The triple bond can be achieved if the alkyl halide is reduced after the reaction is done.
In the following examples, acetylide ion displaces primary halides.
If the back-side approach is hindered, the acetylide ion can abstract a protons, which can be eliminated by the E2 mechanism.
Adding an ethyl group and a hexyl group to acetylene can make it.
Either way, this can be done.
Adding the hexyl group is what we begin by.
Ethchlorvynol is similar to other carbanions in that it has strong bases and strong nucleophiles.
They can add to the carbonyl tissue of the central nervous system by enhancing its distribution into the fatty addition.
The carbon atom has an equal amount of positive and negative charge.
The positively charged carbon has a negative charge on the oxygen atom.
The alkoxide ion is a strong base.
The alcohol is given by a sequence of separate protons that are separated by water or acid.
The C " O double bond of a carbonyl group resembles the C " C double bond of an alkene.
The carbon atom has a partial positive charge.
This addition to a carbonyl group can be served by an acetylide ion.
An alkoxide ion is formed by adding the acetylide ion to the carbonyl group.
The alkoxide is given the alcohol by the addition of dilute acid.
After the protonsation step, a primary alcohol with one more carbon atom than the acetylide is given.
The carbonyl group of the aldehyde was bonded to the acetylide and alkyl group of the secondary alcohol.
A ketone has two alkyl groups on its carbonyl carbon atom.
A tertiary alcohol is given by the addition of an acetylide.
The two alkyl groups originally bonding to the carbonyl group in the ketone are the OH group.
An ethyl group and a six-carbon aldehyde are needed to form the secondary alcohol in acetylene.
The alkylation by the ethyl group would be interfered with by the OH group.
We should add the less reactive ethyl group first and then add the alcohol group later in the synthesis.
If a synthesis requires more than one reagent.
In some cases, we can create a carbon-carbon triple bond by removing HX from a dihalide.
An alkyne may occur under strongly basic conditions.
Many examples of dehydrohalogenation of alkyl halides have already been seen.
The second step is new because it involves dehydrohalogenation of a vinyl halide.
The second dehydrohalogenation can only happen under extremely basic conditions, such as fused (molten) KOH or alcoholic KOH in a sealed tube.
The double dehydrohalogenation is done with sodium amide.
The amide reaction takes place at a lower temperature than the hydroxide ion.
The use of either KOH or sodium amide at these elevated temperatures can lead to side reactions and rearrangements.
Poor yields are common.
Products that are not prone to side reactions are formed from the following reactions.
The most stable internal alkyne is usually given by the KOH elimination.
The terminal alkyne is caused by the acetylenic hydrogen being deprotonated by the amide ion.
The terminal has a acetylide ion.
A foul-smelling compound of formula C9H8 is called X major product.
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