1H NMR of cyclohexanecarbaldehyde

Question

Can someone please explain how to assign the 1H nmr peaks of substituted cyclohexane group? I am more familiar with interpreting substituted benzene. I get that the signal near 10ppm refers to the aldehyde group. The rest of the signal refers to the hydrogens on the cyclohexane group. I also understand that the assignment of Hb (see the picture below).

However, I don't know how I would compare the relative chemical shift between the remaining hydrogens. Since there are multiple peaks, the "Hd"s are chemically distinct. That is also observed when we use do the NMR analysis with higher resolution (See the second spectrum below). Indeed, I have 1H NMR results with slightly better resolution. For "Hc" and "Hd"s, we can indeed resolve 4 peaks corresponding to signals at ~1.9, ~1.8, ~1.7 ~1.3ppm. The integration for these peaks are 2:2:2:4.

How would you assign the chemical shift for those 4 peaks?

the data is coming from http://www.hanhonggroup.com/nmr/nmr_en/B21091.html

Here is spectrum with a better resolution.

The picture is retrieved from https://spectrabase.com/spectrum/LEvG58hCD1J?a=SPECTRUM_LEvG58hCD1J

Answer 1

How would you assign the chemical shift for those 4 peaks?

Since there is overlap between some of the resonances I would run a COSY experiment to resolve the peaks and find correlations, and make assignments on that basis. A number of things can complicate assignment. First, the CHO group can be in axial or equatorial positions, leading to two overlapping subspectra under slow exchange. In addition you have different shifts for geminal Hs, in equatorial/axial positions, separated by ~0.5 ppm (equatorial further downfield), with resolution into two peaks depending on the exchange time (e.g. temperature). The equatorial/axial H are coupled with a relatively strong J-coupling (~12 Hz). The chemically equivalent hydrogens are not magnetically equivalent, but this is not very important since long distance couplings are small.