Alkynes

It takes alkynes to make a world

Nomenclature: C_nH_n

ethyne

All the alkynes are linear e.g.

It has one s bond and two p bonds orthogonal to one another in the triple bond. See diagram above.

Physical properties:

Mpt's and Bpt's are a little higher than the corresponding alkanes and alkenes.

Name each compound by the IUPAC system:

 

Chemical properties:

1. Additions: These are similar to alkenes; electrophilic or free radical. The intermediate double bond compound can usually be isolated.

Prop-1-yne will add to:

a) Hydrogen Bromide

b) Bromine

The bromine adds in a similar way to the alkene but because of the steric hindrance the second bromine adds trans to the first bromine.

2. 1-Alkynes as acid

We can see from the results table that ethyne is less acidic than ethanol. The hydrogen can be removed by Sodium azanide (NaNH₂) in liquid ammonia.

Also, with the use of a grignard reagent;

Preparation of alkynes :

1. Eliminations. The elimination of bromine.

2 Carbide hydrolysis.