For this molecule, C=C(C)C(=O)OCC[N+](=O)[O-] 2571991, JChem/CXCALC 15.5.4 deprotonates the methylene carbon alpha to the nitro group around pH 7.2 (see attached). I would be interested to know what data you used to parameterize this. Do you have a reference please?
I'm sorry to seem impatient, and perhaps you feel we should just ignore nitros, but some drugs have nitros, e.g. NITHIAMIDE and SIVIFENE and this is thus a serious problem for us. No way these should be carbanions. Can you please check and let us know?
Thanks for reporting this pKa bug.
Sorry for the week long lack of answer but unfortunately I received your question only today due to some technical issue.
Based on your feedback an improved version will be released asap, probably on the next week.
The pKa value of a "similar" molecule and its experimental pKa value is given on the attached figure.
The carbanion species will be present in circa 7% at pH=7.2 according to the predicted pKa value of the molecule you brought up in this discussion.
Hoping we were able to help you.