If there are two chains of equal length,choose the chain that has the highest number of substituents. CH CH: CH3 CH一CH CH: CH- CH2 CH- CH-CH,CH CH- CH- CHCH; CH3 CH-CH3 CH,CH-CH CH CH3 wrong correct seven-carbon chain,but only three substituents seven-carbon chain,four substituents Numbering starts at the end nearest a substituent so that the alkyl substituents have as low numbers as possible CH methyl CH CH CH2 CH. CH ethyl CH CH,CH: CH- CH CHCH: CH CH- CH CH, CH- CH CH. methyl CH, methyl incorrect correct 3-ethyl-2,4,5-trimethylheptane Ch03 Alkanes (landscape) Page 4Ch03 Alkanes (landscape) Page 4 If there are two chains of equal length, choose the chain that has the highest number of substituents. Numbering starts at the end nearest a substituent so that the alkyl substituents have as low numbers as possible