Question

In a biomaterial, formation of hydrogen bonds on alcoholic groups will lead to a ________________________________________.

• A. shift in the infra-red peak around \(1700\ \text{cm}^{-1}\)
• B. shift in the infra-red peak around \(2800\ \text{cm}^{-1}\)
• C. broadening of the infra-red peak around \(3500\ \text{cm}^{-1}\)
• D. disappearance of the infra-red peak around \(1700\ \text{cm}^{-1}\)

Hint:

- Hydrogen bonding broadens and usually red-shifts the \( \mathrm{O\!-\!H} \) stretching band in IR spectra (\(3200\!-\!3600\ \text{cm}^{-1}\)). - Peaks near \(1700\ \text{cm}^{-1}\) are typically \( \mathrm{C=O} \) stretches, not related to \( \mathrm{O\!-\!H} \) bonding.

Answer 1

The Correct Option is C

Step 1: Alcoholic \( \mathrm{O\!-\!H} \) stretching typically appears as a broad band around \(3200\!-\!3600\ \text{cm}^{-1}\).
Step 2: Hydrogen bonding strengthens intermolecular interactions and spreads the vibrational energy levels, causing the \( \mathrm{O\!-\!H} \) stretch to broaden and shift to a lower wavenumber region near \( \sim 3500\ \text{cm}^{-1}\).
Hence the spectrum shows \emph{broadening} around \(3500\ \text{cm}^{-1}\).