And so we gots....H_3C-CH=CH-CH_3 versus H_2C=CH-CH=CH_2. The pi-"bond" of the former creature is LOCALIZED between C_2 and C_3...and of course this could give rise to 2 geometric isomers, which are?
The pi-"bonds" of the LATTER are delocalized over 4-centres...certainly addition of 1 equiv HX would give rise to 1,4-"addition" to some extent....