[ksp]

The compound formula is C10H16O2, IR says carboxylic acid, C-NMR suggests a terminal methylene

I think that H(B)/H(C) (which are bound to the same carbon, CH2@~110ppm) is a terminal methylene that is part of a H2C=C(CH3)C- group. I was wondering about the separation between the two signals, why are they so far apart? There appears to be some coupling to what looks like a distant methyl group, so I don't think the acid is there. What else could it be?

Also, the H(E)/H(F) signals are both bound to the same carbon (CH2) and they are adjacent to the carboxylic acid. It is also the case that H(E) and H(F) see different protons in the cosy spectrum, so it cannot be a HO2C-CH2- group can it? the CH2 group has to be part of a rigid ring, what else would explain the large separation of signals?

Thank you

[MOTOBALL]

You should calculate the total number of rings + double bonds from the molecular formula; this will aid in drawing possible structures to match the nmr data.