Question

5. Draw the ring-flip and determine their relative energies. --CH O (CHDC- OH 6 pts 6. Draw the conformations of the following compound and rank their relative stability.

Answer 1

5-

• this structure has locking group that is C(CH3)3(t-butyl group) and it always prefer an equatorial position in a ring. So it will not show ring flipping phenomenon. although if you want we can draw the structure. the golden rule in making flipping structure is whatever the groups are on equatorial position become axial and vice-versa.
• heavy groups always prefer equatorial positions to get rid of 1,3 di- axial interaction.
• this rule is very strict for t-butyl group that even if the structure has 2 same groups like this it can force the ring to pucker into a twist- boat structure so that both can be in the equatorial position

The energy difference between axial and equatorial position of each group is given below in a table.

1-	t-bu	22.8KJ/MOL
2-	Br	2.4 KJ/MOL
3-	OH	4.2 KJ/MOL
4-	CH3	7.6 KJ/MOL
	Total energy difference	37 KJ/MOL

(57 7 CH2 OH OH (H₂ - Locking group. Highly untolle tighly untable

6-

• a sigma bond can show many confirmations around it due to free rotation
• a molecule such as ethane shows nearly 12kj/mol of higher energy in its eclipsed confirmation than that of staggered conformation and here it has many big substitutes which will lead it to higher torsional strain(eclipsed strain) making it highly unstable in that form.
• the staggered conformation having two big substituents on the 180-degree angle is the most stable conformation
• eclipsed structure (V) is the least stable because of strain between methyl groups and electron density of benzene ring.
• although Fluorine does not show that much steric hinderance but it sometimes can affect the structure due to INDUCTIVE EFFECT.

boml 1. on aroung or ofnot There will be free dobition aroung or bond. Newman bejetion (for simplification) MA Dett (1) . 02 لر (ت) ZH H - Leclipsodyt eclipsid. tro [ui) ft م ) . ч LOGÓ Hd и и A Peclipsed 1. (Staggeren (skogeiet)