1. What is the final product when ethyne reacts with HCN?
2. Is hydrogenation of alkenes and alkynes a syn addition?

1 CHCH +HCN ----------CH2CH(CN)
2)Yes hydrogenation of alkene is a syn addition.The unsaturated substrate is chemisorbed onto the catalyst, with most sites covered by the substrate. In heterogeneous catalysts, hydrogen forms surface hydrides (M-H) from which hydrogens can be transferred to the chemisorbed substrate.Since it is a surface phenomena the reaction takes place with syn aaddtion