丁烷有2种同分异构体，戊烷有3种同分异构体？

丁烷有2种同分异构体,
戊烷有3种同分异构体,
己烷有4种同分异构体，
n烷有n-2种同分异构体

对的 丁烷有2种同分异构体，戊烷有3种同分异构体

没错。我写一下：CH3CH2CH2CH3 (CH3)3CH
CH3CH2CH2CH2CH3 CH3CH(CH3)CH2CH3 (CH3)4C

戊烷分子式c5h12,其同分异构体有三种：
1.ch3-ch2-ch2-ch2-ch3
正戊烷
2.ch3-ch(ch3)-ch2-ch3
异戊烷（2-甲基丁烷）
3.c(ch3)4
新戊烷（22-二甲基丙烷）
己烷：
ch3-(ch2)4-ch3
ch3ch(ch3)-(ch2)3-ch3
ch3ch2ch(ch3)-(ch2)2-ch3
ch3ch(ch3)ch(ch3)ch2ch2ch3
ch3ch(ch3)ch2ch(ch3)ch2ch3
ch3ch(ch3)ch2ch2ch(ch3)ch3
ch3ch(ch3)ch(ch3)ch(ch3)ch3
庚烷：
ch3-(ch2)5-ch3
(ch3)2-ch-(ch2)3-ch3
ch3ch2ch(ch3)ch2ch2ch3
(ch3ch2)3ch
(ch3)3-c-ch2ch2ch3
(ch3ch2)2-c-(ch3)2
(ch3)2-ch-ch(ch3)-ch2ch3
(ch3)2-ch-ch2-ch-(ch3)2
(ch3)3-c-ch-(ch3)2