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CH 220 1st Edition Lecture 8Outline of Current Lecture I. AlkynesII. Electrophilic Addition of AlkynesIII. Reaction mechanismsIV. Carbocation StabilityCurrent LectureI. Alkynesa. Any hydrocarbon that contains a carbon-carbon triple bond is an alkyneb. General hydrocarbon rules apply with ‘-yne’ as a suffix indicating an alkynec. Numbering of chain with triple bond is set so that the smallest number possible is assigned to the first carbon of the triple bondd. Triple bonds have importance over double bonds if they both appear in some compoundsII. Electrophilic Addition of Alkynesa. General reaction mechanism of electrophilic additionb. 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 Mechanismsa. A reaction mechanism is the story of how a reaction happens at the molecular levelb. A curved arrows show reaction in motionc. Straight arrows show end productd. Look for the double bond to identify the starting pointThese 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.IV. Carbocation Stabilitya. Some carbocations are more stable than othersb. The more carbons that are attached to the carbocation, the more stablec. This comes into play when deciding which way the double bond opens up to bond to the hydrogen, and which stays without a bond and acquires a positive charged. The more carbon neighbors the positive charge has, the more likely it is to be in that locationThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a


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