Question

Which substituent has the smallest magnitude for 1,3 diaxial interaction?

		-CH3
		-CH2CH3
		-CH(CH3)2
		-C(CH3)3

Answer 1

8 13- Diasial interaction. cyclohexane molemle ways represented in chrain. formation to gain stability: always contan ma tion a Ha Ha HH ve De XA H H Ha # M axial bon att He Ha Ha He = equato Chair arial con formation. bon. When the axial substitue inter feres with axial hydrogens. and Co. This s inter intent ference is called 1,3 - dia e interaction. 63 am substituent. ydrogens on 1. H HMy flipping #tu + ακα- H 1 C-H H -1,3-diarial interaction equatorial more stable.. by 1.70 Kcal/mol 1-methyl cyclohexane 1,3-diazial interaction is also known as gauche - butane interaction. * With inerease in bulkiness on axial position, 1,3-diaxial int the difference is 1.7 kcaly increases o for CH3 group, the differene – CH₂ CH₂ group the difference is 175kcay mon The difference in en. only 175 kcal/mol (compare to methy at 1.70 kcal/mol). This is because the only significant dianial interactions are with the –CH2 group. The ethyl group can rotate

such that the cHa group pro away from the wing, Dhave it not lead to any significant en Strain, CHE CH₂ group proints from Hipping ing 5 m си, сиз х 4 # equatorial stabilised by 0 Fon iso-propyl (-CH(CH3)2), the energy is 2115 x cal/mol 1.75kcal/mol different H- 13 Lukt-CH₂t a conformation is still Where bond is V available the e-H over the axial Alpping o for tert-buty! (- (043)) . 2.15 Keal somos difference is 4.9 kcal/mol -butyl (c(+43) 3) the équatorial stabilised by steric energy Clash 4 _CH3 CH3 143 This is biggie. flipping is unavoidable LÀ ANH PC-CH2 23 2 axial equatorial Because of this huat stable Stability, we his huge difference in often consider on cyclohexane to be locked in equatorial position. t-butyl substituenti • Decreasing order of 43-diarial interaction ginen a by substituents - c(CH3)3)-CH(CH3)2 - CH₂ CH3)-CH3 0 So CH3 group has the smallest magnitude for 13- dianial interaction