Which of the following give a NEGATIVE Tollens' test (no silver mirror)? Take adenosine as the beta-N9-glycoside of D-ribofuranose with adenine.

AFree D-ribose
BAdenosine
CMethyl beta-D-glucopyranoside
DD-fructose

Answer: B, C

A positive Tollens' test needs a free hemiacetal (anomeric) carbon that can open to an aldehyde, or a ketose that isomerises through an enediol. In adenosine the anomeric C-1 of ribose is bonded to nitrogen of adenine and in the methyl glycoside to OCH3, so neither can open up. Free ribose and fructose are reducing.

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