Question

The absorbance spectrum of 1,3-butadiene displays an absorption in the UV region (λmax = 217 nm), while the absorption spectrum of 1,2-butadiene does not display a similar absorption because the bonds in 1,2-butadiene are ______.

Answer 1

Cumulative.

Step-by-step explanation:

1,2- butadiene had the chemical structure which is written as CH2=C=CHCH3. If you look at the structure very well, you will notice that the two double bonds follow each other with no space in between them. This kind of compounds is known as an allene.

For a compound to be Ultraviolet (uv) active it must be conjugated that is to say the double bonds must must be cumulative for instance now 1,3-butadiene which the structural formula CH2=CH-CH=CH2. As you can see, there is a space in between the double bonds in the 1,3- butadiene compound.

Therefore, 1,2- butadiene is not conjugated so it is uv inactive.

Answer 2

Cumulative

Step-by-step explanation:

Cumulative double bonds usually consists of three contiguous carbon atoms joined by double bonds such as in an allene. They are also called twinned double bonds. Allenes are not as stable as conjugated systems such as 1,3-butadiene.

Conjugated systems show an absorption maxima in the UV-visible portion spectrum at longer wavelengths due to conjugation of the double bonds which shifts the absorption maxima to longer wavelengths. This is known as Bathchromic shift.