Chapter 14.SE, Problem 48AP

The following ultraviolet absorption maxima have been measured:

1,3-Butadiene 217 nm

2-Methyl-1,3-butadiene 220 nm

1,3-Pentadiene 223 nm

2,3-Dimethyl-1,3-butadiene 226 nm

2,4-Hexadiene 227 nm

2,4-Dimethyl-1,3-pentadiene 232 nm

2,5-Dimethyl-2,4-hexadiene 240 nm

What conclusion can you draw about the effect of alkyl substitution on UV absorption maxima? Approximately what effect does each added alkyl group have?