Question

The 1H NMR spectrum for the cyclohexyl ester shown below has a peak at 4.91 ppm due to
the proton indicated in bold. The signal is a triplet of triplets (tt) with 3J values of 8.8 Hz and 3.8
Hz. Use the coupling constant values and the Karplus relationship to determine whether the
ester group is axial or equatorial.

The 1H NMR spectrum for the cyclohexyl ester shown below has a peak at 4.91 ppm due to the proton indicated in bold. The signal is a triplet of triplets (tt) with 3J values of 8.8 Hz and 3.8 Hz. Use the coupling constant values and the Karplus relationship to determine whether the ester group is axial or equatorial.

Answer 1

The ester group have equatorial position as it's 3J values gave dihedral values 0 and near to zero (1.8761) and also it's high chemical shift value indicate the presence of equatorial position of ester group.

3gp = 8.5 (08²6 - 0.28 8.8 - 8.28 = 8.5 Los & 8.52 = cos & 4.002 = Cos& 1.0009 Cos & a $1.002 = ps Cos-11.000 fi oo 35812 8.5 (6820-0.28 .3.8 -0.28 = 8.5 Cosad 3.52 a Cos2o (os o 2 $3.52 = 1.8761 o= Cos 1.8761 0 = 1. 240 So & is almost mear to oo among two possible configuration Hence 0 0 (tt) и L (but this proton have less Svalu than 4.91) This confirmation has strong possibility and also gave triplet of triplet as it have four sorrounding proton on two adjaunt corbon.