Q157
General ScienceChemistry
The chopping of an onion makes one cry because of the chemical containing
- a.Sulphur
- b.Chlorine
- c.Bromine
- d.Nitrogen
Answer: (A) Sulphur
Cutting an onion breaks its cells, and the enzyme alliinase acts on sulphur-containing amino acid sulfoxides to produce sulfenic acids, which are converted into the volatile gas syn-propanethial-S-oxide ($C_3H_6OS$), the lachrymatory (tear-causing) factor; in the eye it forms traces of sulphuric acid that irritate the tear glands. Garlic's smell is similarly due to the sulphur compound allicin. Chlorine and bromine compounds are used in tear gas but are not found in onions. Chilling the onion or cutting it under water reduces the effect.