Question

Which is more polar, 4-Methylcyclohexanol or 4-Methylcyclohexane? Explain using functional groups and give the basic NMR, IR, and Mass spectroscopy for both compounds

Answer 1

4- Methylcyclohexanol is more polar than 4- methylcyclohexane. Dipole moment is a vectror quantity, when a molecule is formed by two atoms with different electronegetivities. Oxygen atm is highly electronegetive , so the compound 4-Methylcycloheanol it is highly polar due to presence of -OH group . But in 4-methylcyclohexane only -CH₃ group is present. As sp³ carbon is less electronegetive, therefore the compound is less polar.

NMR

4- Methylcyclohexanol

1. three proton singlet (due to methyl group) upfield

2. one proton singlet ( due to - OH group, downfield)

3. one proton triplet ( attach in C4 )

4. two proton doublet  (for the hydrogen close to -OH group, downfield)

5. two proton doublet 7.2 (for the hydrogen close to -CH₃ group, upfield)

4- Methylcyclohexane (total 5 different signals)

1. three proton singlet (due to methyl group, upfield)

2. one proton triplet ( attach in C1 )

3. two proton triplet ( C2 and C6)

4. two proton triplet (C3 and C5)

5. one proton triplet (C4)

IR

4- Methylcyclohexanol

1. near to 3330 cm^-1 for -OH group,

2. 2996 cm^-1 C-H streching.

4- Methylcyclohexane

1. close to 3000 cm^-1 C-H streching for cyclohexane

2. 2872 cm^-1 for C-H streching for -CH₃ group

mass

4- Methylcyclohexanol

It will give a base peak of m/z= 57 , and by loosing water it will give another intense peak m/z= 96  

4- Methylcyclohexane

It will give a base peak of m/z = 70, by the loss of ethylene