Acidity of Alkynes Terminal alkynes are acidic,the end hydrogen can be removed as a proton by a strong base. E.g CH,CH2一C=C一H+Na+NH, CHCH,-C=C:-Na+NH but-1-yne,a terminal alkyne sodium amide sodium butynide C=C一H NaNH2 C=C:-Na+NH, cyclohexylacetylene sodium amide sodium cyclohexylacetylide CH,一C=C-CH NaNH2> no reaction (no acetylenic proton) but-2-yne,an internal alkyne Synthesis of Alkynes The carbanions produced are called acetylides,and are strong nucleophiles. R-C=C: S2, R-C=C-R'十X (R-X must be a primary alkyl halide) They can react in SN2 displacements of halides or tosylates from primary unhindered substrates to produce internal alkynes. Ch09 Alkynes(landscape) Page 5Ch09 Alkynes (landscape) Page 5 Acidity of Alkynes Terminal alkynes are acidic, the end hydrogen can be removed as a proton by a strong base. E.g. Synthesis of Alkynes The carbanions produced are called acetylides, and are strong nucleophiles. They can react in SN2 displacements of halides or tosylates from primary unhindered substrates to produce internal alkynes