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5.11 a) b) 5.12 The procedure for naming alkenes is similar to that used for alkanes except for the following: 1) The longest continuous chain must include the double bonded carbons. 2) The suffix for alkenes is -ene. 3) The root is numbered from the end that gives the lowest possible number to the first carbon of the double bond. The number of the first carbon is used in designating the position of the double bond. a) The longest carbon chain containing the double 4 5 bond has 6 carbons, so the root name is hexene. The root is numbered from the end that will give the lowest possible number to the double bond. The correct name 2 3 6 of this compound is 1 b) Here the root is a 7 carbon ring with three double 7 bonds, so the root name is cycloheptatriene. The 6 numbering must start with one of the carbons of a 1 double bond and the other carbon of that double bond 5 must be at position 2. The numbering shown gives the lowest numbers to the double bonds and then the 2 4 3 substituent, so the name of the compound is c) In a cycloalkene, the numbering must start with one of the carbons of the double bond and the other carbon of 3 the double bond must be at position 2. In this case, the end of the double bond to use as position 1 is chosen to 2 give the ethyl group number a lower number. The name 1 is 3-ethyl-1,2-dimethylcyclopentene. 68