\(\beta \)-carotene is involved in the formation of vitamin A. Its sources include carrots, broccoli and dark, leafy vegetables. Its structure is shown below.

Explain whether\(\beta \)-carotene absorbs ultraviolet or visible radiation.

extensive conjugation of (C=C) double bonds / alternate single and double (carbon–carbon) bonds / involving delocalization of \(\pi \) electrons;

less energy is required (to excite the electrons);

absorption occurs in the visible region;

Candidates recognised that \(\beta \)-carotene consisted of conjugated C=C double bonds but often answered, that because of this it absorbed ultraviolet radiation. Few candidates could explain that less energy was required to excite the electrons due to the conjugation.