(2E)-butenoyl-CoA + FADH2 => butanoyl-CoA + FAD + H(+)
(2e)-butenoyl-coa + fadh2 => butanoyl-coa + fad + h(+)
(2E)-butenoyl-CoA + FADH2 => butanoyl-CoA + FAD + H(+)
(2e)-butenoyl-coa + fadh2 => butanoyl-coa + fad + h(+)