Question

Question: Which of the bonds shown in red are expected to have IR-active stretching frequencies?

Short answer

Answer

a. In the first case, C-C bond exhibit IR stretching frequency due to different environment.

b. C-C bond has a different environment and hence, exhibits IR stretching frequency.

c. C-C triple bond has different environment thus, it has IR active stretching frequency.

d. C-H bond has electronegativity difference thus, it exhibits the difference in dipole moment. So, we have IR active stretching frequency.

e. C-C bond has a different environment. Hence, it will show IR active stretching frequency.

f. C-C bond has a different environment. Hence, it will show IR active stretching frequency

g. C-C triple bond have different environment. Hence, it will show IR active stretching frequency.

h. C-C double bond have different environment. Hence, it will show IR active stretching frequency.

i. C-H bond have different environment. Hence, it will show IR active stretching frequency.

j. C-C bond do not have have different environment. Hence, it will not show IR active stretching frequency.

Step-by-step solution

IR active bonds

If the bond between two atoms is polar, then it is IR active. The surrounding atoms/groups to an atom also decide the polarity of a bond.

Explanation

Bonds having non-zero dipole moments will exhibit IR absorption. Bonds present in a symmetric environment will exhibit weak absorption.

a. In the first case, C-C bond exhibit IR stretching frequency due to different environment.

b. C-C bond has a different environment and hence, exhibits IR stretching frequency.

c. C-C triple bond has different environment thus, it has IR active stretching frequency.

d. C-H bond has electronegativity difference thus, it exhibits the difference in dipole moment. So, we have IR active stretching frequency.

e. C-C bond has a different environment. Hence, it will show IR active stretching frequency.

f. C-C bond has a different environment. Hence, it will show IR active stretching frequency

g. C-C triple bond have different environment. Hence, it will show IR active stretching frequency.

h. C-C double bond have different environment. Hence, it will show IR active stretching frequency.

i. C-H bond have different environment. Hence, it will show IR active stretching frequency.

j. C-C bond do not have have different environment. Hence, it will not show IR active stretching frequency.