Dear colleagues,
i read of an article, syn comm 23(10),1351-1356(1993)and am quite
puzzled with the results obtained.the following is the summary of the
paper:
Nitration of 2,5- Dimethoxybenzaldehyde  [ named as A]

1) A ---------.> 3,5- Dimethoxy-2-nitrobenzaldehyde (64%) +
                     2,5- Dimethoxy-4-nitrobenzaldehyde (26%)

2) A---------->  MIXTURE OF mono, di and trinitro compound

3) A----------> 3,5- Dimethoxy-2-nitrobenzaldehyde (60%) +
                   2,5- Dimethoxy-4-nitrobenzaldehyde (29%) +
                   2,5- Dimethoxy-3-nitrobenzaldehyde (5%)
condition for
1)70%  HNO3 as solvent and nitrating agent, stirred at RT for 3 hrs.
3)70 % HNO3 Et20 as solvent + acetic acid, stirred at RT for 30 hrs.
my question is ,
why should 3,5- Dimethoxy-2-nitrobenzaldehyde be the major compound in
both cases in viewof the fact that it may be affected by steric
hindrance.(moreover -CHO is a meta director)
my opinion is  2,5- Dimethoxy-3-nitrobenzaldehyde should be the major
product.
could anyone please offer me some possible explanation? and is there any
other condition where one can get
2,5- Dimethoxy-3-nitrobenzaldehyde as major product?

Grateful to get some reply.
Thanx in advance,
Barnabas


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