achieve homework week 5&6 no.4

[Emily Widjaja 3A]

Hello,

for the question asking about the bond length: The observed carbon–oxygen bond lengths in carbamate are both 128 pm, whereas the observed carbon–nitrogen bond length is 136 pm. Expected values are shown in the table:

Bond Expected bond length (pm)
C−O 143
C=O 112
C−N 152
C=N 127

Why is one of the correct choices "The carbon–oxygen bonds have ample C=O bond character."? I thought the observed carbon oxygen bond length is closer to the bond length of c-o (difference by15 pm), as the difference in bond length with C=O is 16 pm. Wouldn't the ample Carbon oxygen bond character be the one whose expected value is closer to the observed value (like how the expected value of C=N is closer to the carbon nitrogen observed bond length)?

[Jenny Han 3F]

I believe that "ample" bond character means that there is sufficient C=O bond character to have made a difference on the overall bond character. Since C=O is 16 pm and C-O is 15 pm from the observed bond length, both the single and double bond character contribute sufficiently to the overall bond length. The bond length may be slightly closer to C-O but C=O bond character still contributed sufficiently to the observed bond length, since the bond length isn't incredibly close to the C-O bond character.