a B CH2CH=CHCH; CH3 H3C CHCH=CH2 CH3 OH HgC CH3 CH3 CH2CH=CHCH; CH2CH=CHCH3 βY aβY O CH2CH=CHCH3 α β γ H3C CH3 Δ O H3C CH3 α CHCH=CH2 CH3 γ O H3C CH2CH=CHCH3 α β γ CH3 H OH H3C CH2CH=CHCH3 α β γ CH3