Q31. - Organic Chemistry

Question

Question: Which of the bond shown in red in each compound or pair of compounds is shorter?

                               a.

                               b.

                               c.

                                 d. 

Step-by-Step Solution

Answer

Answer

a. In the given compound, the triple bond is shorter compared to the double bond.

 

b. The double bond adjacent to nitrogen is shorter than the single bond adjacent to nitrogen.

 

c. The aldehyde group’s hydrogen (CHO) is shorter than hexanol’s hydrogen.

 

d. The N-H bond lying close to the double bond is shorter than the one adjacent to the single bond.

Step-by-Step Solution Step 1: Effect of hybridization on bond length

The bond length reduces as the s-character elevates in hybridization. So, the order of bond length is $\mathrm{sp}>{\mathrm{sp}}^2>{\mathrm{sp}}^3$.

Step 2: Reasons for the shortening of bonds with s-character

The reasons are as follows:

 

• The s-orbital is close to the nucleus.
• Due to the spherical shape of the s-orbital, the attraction with the nucleus is symmetrical.
• Therefore, the electronegativity of sp orbital is greater than that of ${\mathrm{sp}}^2$, followed by,${\mathrm{sp}}^3$. This increases the attraction of the shared electrons (bond electrons) and decreases the bond length.

 

Step 3: Determination of shorter bond

a. The triple bond is formed by sp hybridization; therefore, the carbon-carbon triple bond is shorter compared to the double bond (formed by ${\mathrm{sp}}^2$ hybridization).

                                      

                                            Hybridization around the carbon atom 

b. The double bond (${\mathrm{sp}}^2$ hybridization) adjacent to nitrogen is shorter than the single bond (${\mathrm{sp}}^3$ hybridization) adjacent to nitrogen.

                                             

                                                      Hybridization around the carbon atom 

c. The aldehyde group’s hydrogen (CHO) is shorter due to ${\mathrm{sp}}^2$hybridization of carbonyl carbon than the cyclohexanol’s hydrogen formed by ${\mathrm{sp}}^3$hybridization.

                                                         

                                                      Hybridization around the hydrogen atom

d. The N-H bond near the double bond is shorter due to ${\mathrm{sp}}^2$hybridization, where the N-H bond near the single bond is longer due to ${\mathrm{sp}}^3$ hybridization.

 

                                                   

                                                         Hybridization around the nitrogen atom