CHEM 203 Lecture Notes - Lecture 19: Birch Reduction, Lindlar Catalyst, Solvated Electron
Document Summary
Technological importance of the semihydrogenation of alkynes, i. e. , in the addition of only 1 molecule of h2 to their systems, as a route to cis-alkenes. Lindlar catalyst: finely divided pd deposited on baso4 particles and modified with sulfur and other substances that moderate the reactivity of pd. Semihydrogenation of alkynes with the lindlar catalyst: conversion of alkynes to cis-alkenes through a syn addition of h2: R1 c imagine that both r groups were alkyls R2 cis isomer note: the cis geometry is a consequence of the syn course of the rx. Unusually high electronegativity of sp-hybridized carbon atoms relative to sp3 and sp2 hybrids, as a result of considerable s-character (50%) in their orbitals: R1 c c h e. n. sp3-c 2. 5 e. n. sp2-c 2. 6 e. n. sp-c 2. 8. Strong electron electron-accepting ability of sp-hybridized carbon atoms. Reactions that reflect the electron-accepting ability of carbon sp-hybrids: the semihydrogenation of alkynes with na/nh3(liq) leading to the formation of trans-alkenes.
