And so we gots....H_3C-CH=CH-CH_3H3C−CH=CH−CH3 versus H_2C=CH-CH=CH_2H2C=CH−CH=CH2. The pi-"bond"π−bond of the former creature is LOCALIZED between C_2C2 and C_3C3...and of course this could give rise to 2 geometric isomers, which are?
The pi-"bonds"π−bonds of the LATTER are delocalized over 4-centres...certainly addition of 1 equiv HXHX would give rise to 1,4-"addition"1,4−addition to some extent....