CHEM 140B Chapter Notes - Chapter 13: Protonation, Stereochemistry, Acetylene
3 Feb 2017
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Ochem textbook notes chapter 13: alkynes- the carbon-carbon triple bond. General formula: cnh2n-2 (same for cycloalkenes: ending: -yne replaces ene, number indicates the position of the triple bond in main chain, alkenyne: hydrocarbon containing both double and triple bond. Double bond is given lowest number if equidistant positions apart: alkynols: alkynes incorporating hydroxy group. Alkynes are relatively nonpolar: has no boiling point; sublimes. Ethyne is linear and has strong, short bonds: sp hybridized, strength: 229 kcal/mol. Alkynes are high-energy compounds: 4 pi electrons in small volume of space; large repulsion so high energy content, react with a release of energy. Terminal alkynes are remarkably acidic: atoms with hybrid orbitals high in s character will be slightly more electronegative, strong bases can deprotonate terminal alkynes to corresponding alkynyl anions. Hs and cs in alkenyls are deshielded, so low-field nmr signals. Alkynyl hs have chemical shifts at relatively high fields. Alkynyl cs absorb in a range between alkenes and alkanes.
