Explain why oleic acid, cis-9-octadecenoic acid, has a lower melting point than its trans isomer, elaidic acid.

Discuss two effects on health of consuming trans fatty acids such as elaidic acid.

kink/shape of cis-isomer prevents molecules packing closely together / reduces area of close contact / OWTTE;

so weaker intermolecular attractions/dispersion/London/van der Waals’ forces;

Accept converse argument based on trans-isomer.

hard to metabolize / accumulates in fatty tissue / difficult to excrete;

increases levels of LDL cholesterol / increases risk of heart disease;

Do not accept “increases level of bad cholesterol”.

Most students correctly identified the compound that combines with fatty acids in triglycerides, but explanations of the lower melting points of cis-isomers usually lacked precision. The relationship between trans-fats and HDL/LDL levels and disorders arising from an unhealthy ratio of these seemed well known, but the difficulty in metabolizing these was rarely mentioned. Candidates either knew, or did not know, the mechanism for free-radical oxidation of fats with very few gaining partial marks; most however could identify a factor relevant to reducing its rate.

Most students correctly identified the compound that combines with fatty acids in triglycerides, but explanations of the lower melting points of cis-isomers usually lacked precision. The relationship between trans-fats and HDL/LDL levels and disorders arising from an unhealthy ratio of these seemed well known, but the difficulty in metabolizing these was rarely mentioned. Candidates either knew, or did not know, the mechanism for free-radical oxidation of fats with very few gaining partial marks; most however could identify a factor relevant to reducing its rate.