Answers to questions on Lipids

(b) Esterification or condensation.

(c)

(d) It will be a liquid. It contains a high degree of unsaturation and the double bonds cause ‘kinks’ in the hydrocarbon chains so that the London dispersion forces between them are lower than for saturated hydrocarbon chains and hence the melting point will be lower.

(e) M_r for iodine (I₂) = 2 x 126.9 = 253.8

25.38 g = 0.100 mol of I₂

One mol of the triglyceride reacts with 9 mol of I₂ (as it contains nine C=C double bonds)

Hence mass of triglyceride = (0.100 x 873.5) / 9 = 9.71 g

2. (a) It contains the typical four membered ring configuration present in all steroids.

(b) Add bromine (or iodine). Cholesterol will decolourise it rapidly as it contains a C=C double bond whereas estradiol does not contain a C=C double bond (so the Br₂ or I₂ cannot add to it). Note that the phenyl ring does not readily undergo addition reactions.

3. The first/upper structure is the cis- form and the second/lower is the trans- form.
They show cis/trans (or E/Z) isomerism.
The trans- form can be formed during the partial hydrogenation of polyunsaturated fattyacids.
It can increase LDL cholesterol, which can increase the risk of heart disease.