# Which ethanol derivatives display the gauche effect?

How many of the following ethanol derivatives of the form $$\ce{GCH2CH2OH}$$ have a more stable gauche conformer compared to their anti conformer?

$$G = \ce{F}, \ce{Cl}, \ce{OH}, \ce{NH2}, \ce{OMe}, \ce{NHMe}, \ce{NMe2}, \ce{NO2}$$

I was sure that $$\ce{F}$$, $$\ce{OH}$$, $$\ce{NH2}$$ and $$\ce{NO2}$$ display the gauche effect. I'm not so sure regarding all the other groups: all of them seem bulky and won't form hydrogen bonds with the $$\ce{OH}$$ group on $$\ce{C}_1$$. How many of the other substituents are capable of displaying this effect? Also, is there a quantitative way to determine if the gauche conformer would be more stable than the anti conformer?

• Nice question, I am pretty sure that ethylene chlorohydrin also has gauche form more stable. Also I think for knowing most stable form we need to optimize the molecular geometry on different levels of quantum chemistry, starting from a conformer halfway between staggered and eclipsed. Levels are like HF/def2-TZVP, PBE-D3/def2-TZVP... Don't know direct way to find that. Further, I think G=NHMe would also form more stable gauche form (not sure). What's the answer given? – Zenix May 19 at 12:14
• The answer is 7. I'm ignoring it for now until I have an explanation. – Aniruddha Deb May 19 at 12:16
• Then, I guess, all except NMe2. – Zenix May 19 at 12:47
• @Zenix More probably NO2 - it would have H-bond but with 6-membered ring. BTW even N(CH3)2 isn't all that bulky. – Mithoron May 19 at 23:45
• See here – Mathew Mahindaratne May 20 at 1:38