Chemistry - STEREO ISOMERISM Question with Solution | TestHub

With X = Z = -OH the compound is ethylene glycol, HOCH₂-CH₂OH : the gauche conformer is stabilized by an intramolecular hydrogen bond between the two OH groups (and by the gauche effect - hyperconjugation from C-H bonds into the σ* of the electronegative substituent), so the gauche form wins over anti. For -CH₃, -C₂H₅ and -Br only sterics operate and the anti form is more stable.