《有机化学精品教学》（汕头大学）Chap 3 Alkene （2012）.pptVIP

Exercise page 53. 3-9 (1), (3), (6) 3-11 (1), (2), (4), (6), (7) 3-13 3-16 (2) (4) 3-17 3-18 p-π conjugated system Section 3 Alkyne Alkynes: Hydrocarbons have the general formula CnH2n-2. These molecules, also called acetylenes, contain carbon-carbon triple bonds. acetylene, (ethyne) Ⅰ. Structure of acetylene Acetylene is a symmetrical compound of the formula HC≡CH. Each carbon is attached to two other atoms: one hydrogen and the other carbon. As in the discussion of alkanes and alkenes, the atomic orbitals of carbon are combined to yield hybrid orbitals, which will do better job of bonding than the unchanged atomic orbitals. Two bonds are need, one for the bond to hydrogen, and another for the bond to carbon. Therefore, we need to combine only two of carbon’s atomic orbitals to give us our hybrids. A combination of the 2s and 2px orbitals will yield a pair of sp hybrids. sp hybrid sp Hybrid orbital sp hybrid orbital: A hybrid orbital made by the combination of one s orbital and one p orbitals sp-1s Overlap sp-sp Overlap Two ?C-H bonds are formed by sp-1s overlap, and one ?C-C bond is formed by sp-sp overlap. The over-lap between the p orbitals (2py-2py, 2pz-2pz) make up of two ?C-C bonds which are vertical to the ?C-C bond by sp-sp overlap. The ?C-C bond and the ? bonds form to the triple bonds of the acetylene. Ⅱ. Isomerism and Nomenclature 1. Isomerism 1) carbon-chain isomerism 2) positional isomerism 2. Nomenclature The naming rules for the alkynes are similar to that used for the alkenes. As the alkynes, the triple bond is designated a position by assigning it number, which is kept as low as possible. 1-butyne CH3–CH=CH–C≡CH 3-pentene-1-yne When both double and triple bonds are present, the compounds are named as ‘enyens’, and the numbers designating the position of the multiple bonds kept as low as possible. If