X R1 R2 C2-C3
O H H 1.55
O Ac H 1.538
O Me H 1.545
Cl,Cl H H 1.556
OCH2CH2O H Br 1.539
CHCH=C(CH3)2 H H 1.508
Table 1: Bond length between C2 and C3 if X is changed [32].