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CH 220 1st Edition Lecture 8 Outline of Current Lecture I. Alkynes II. Electrophilic Addition of Alkynes III. Reaction mechanisms IV. Carbocation Stability Current Lecture I. Alkynes a. Any hydrocarbon that contains a carbon-carbon triple bond is an alkyne b. General hydrocarbon rules apply with ‘-yne’ as a suffix indicating an alkyne c. Numbering of chain with triple bond is set so that the smallest number possible is assigned to the first carbon of the triple bond d. Triple bonds have importance over double bonds if they both appear in some compounds II. Electrophilic Addition of Alkynes a. General reaction mechanism of electrophilic addition b. An attack on electrophile (such as HBr) by  bond of alkene – a hydrogen atom on HBr is attacked by pi electrons from the nucleophilic double bond, forming a C-H bond. This leaves the other carbon atom with a positive charge and a vacant p orbital. Two electrons from the H-Br bond move onto bromine, making a bromide anion. c. Carbocation is an electrophile, reacting with nucleophilic bromide ion. The Bromide ion donates an electron pair to the positively charged carbon atom, forming a C-Br bond and yielding the neutral addition product. III. Reaction Mechanisms a. A reaction mechanism is the story of how a reaction happens at the molecular level b. A curved arrows show reaction in motion c. Straight arrows show end product d. Look for the double bond to identify the starting point These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.

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