First Year, Organic Tutorial -2
1) Write stable conformations of the following molecules
a) b) c) d)
Me OH
i-Pr
2. Examine the following structures and predict whether the red colored group is axial or
equatorial. Assume all six-membered rings are in the most stable conformation.
Ans: A-ax; B- eq; C – ax; D – eq; E – eq; F – ax; G – ax; H –ax
3. Which one of the following molecules forms epoxide?
a) OH b) OH
X X
4. Draw the configurational and conformational isomers of 1,2-dimethyl cyclohexane and
comment on their relative stability and chirality.
Hint: cis exists (a,e & e,a) in two forms and chiral but they are non resolvabale cause the
flipped structure leads to superimposable mirror image of the parent structure as the
potential energy barrier is too low for flipping. Trans is optically active.
5. Draw the configurational and conformational isomers of 1,3-dimethyl cyclohexane and
comment on their relative stability and chirality.
Hint: The cis iosomers are meso(achiral) due to the presence of plane of symmetry. The
trans form (e,a & a,e ) are chiral.
6. “Both cis- and trans- isomers of 1-bromo-2-chloro-cyclohexane are chiral and
resolvable” explain?
7. Deamination of cis-2-amino-cyclohexanol and trans-2-amino-cyclohexanol with HNO2
yields two different sets of products as depicted, explain the results?
CHO O
HNO2
cis-2-amino-cyclohexanol +
CHO
HNO2
trans-2-amino-cyclohexanol + O
8. Which of the following substrates will undergo base catalyzed elimination readily and
why?
OTs OTs
tBu tBu
9. Reactions with sodium thiophenoxide (PhS-Na+) in aq. EtOH, cis-4-t-butylcyclohexyl
bromide reacts about 60 times faster than the corresponding trans isomer, suggest a
proper reason for the phenomena?
1. 10. For each of the compounds A through H indicate the number of gauche butane
interactions present in the most stable chair conformation.
ans: A-0; B-2; C-0; D-0; E – 3; F – 1; G -2; H-3
11. How many Gauche-Butane interactions are there in the following molecules and show the
connectivity.
Me Me Me
Me
Ans: Molecule 1 = 4GB (one axial substitution counts for 2); Molecule 2 = 3GB;
Molecule: 3 = 5GB
Me Me Me
Me
4GB 3GB 5GB
12. Predict the structure of most stable conformer for cis and trans 1,3-ditertbutyl
cyclohaxane?
tBu
But tBu
Ans: tBu
13. Cis-1,3-cyclohexane-diol is more acidic than trans-1,3-cyclohexanediol. Suggest a
conformational argument to account for this observation.
Hint: Acidity is related to conformation and energetics of the conjugate base. The more
stable the conjugate base more acidic the compound is. In case of the cis-isomer the
conjugate base is stabilized by intramolecular H-bonding which is not possible for trans
isomer.
