Q5 · CSIR-NET Chemistry, June 2017
Paper: CSIR-NET June 2017 · Subject: Organic Chemistry · Chapter: Natural Products · Topic: Carbohydrates · Marks: 2 · Difficulty: Hard
The major product formed in the reaction of D-glucose with $\mathrm{ZnCl_2}$ in MeOH is a methyl glucopyranoside (A or B). The structure of this product and the molecular orbital interaction present between ring-oxygen and the anomeric C-O bond responsible for its stability, respectively, are 
A B
A B(a)A and $n \rightarrow \sigma^{*}$
(b)A and $n \rightarrow \sigma$
(c)B and $n \rightarrow \sigma^{*}$
(d)B and $n \rightarrow \sigma$
Answer
Answer: C ✓ checked by 4AB · confidence high
Explanation
Fischer glycosidation under thermodynamic control favours the α-anomer B (axial OMe). It is stabilised by the anomeric effect: donation from a ring-O lone pair into σ*(C1–OMe), n → σ* (c).
Study loop for Natural Products