Which shows an O–H stretch at a larger wavenumber: ethanol dissolved in carbon disulfide or an undiluted sample of ethanol?

검증된 단계별 안내

Understand the concept of hydrogen bonding: The O-H stretch in an IR spectrum is influenced by hydrogen bonding. Stronger hydrogen bonding lowers the wavenumber of the O-H stretch due to the weakening of the O-H bond.

Analyze the environment of ethanol in carbon disulfide: When ethanol is dissolved in carbon disulfide (CS₂), a non-polar solvent, hydrogen bonding between ethanol molecules is disrupted because CS₂ does not participate in hydrogen bonding.

Analyze the environment of undiluted ethanol: In an undiluted sample of ethanol, ethanol molecules are in close proximity and can form strong intermolecular hydrogen bonds with each other.

Compare the effects on the O-H stretch: In the case of ethanol dissolved in CS₂, the O-H bond is less involved in hydrogen bonding, so the O-H stretch appears at a higher wavenumber. In undiluted ethanol, the strong hydrogen bonding shifts the O-H stretch to a lower wavenumber.

Conclude: Ethanol dissolved in carbon disulfide shows an O-H stretch at a larger wavenumber compared to undiluted ethanol due to the absence of significant hydrogen bonding in the dissolved state.

비슷한 문제에 대한 검증된 영상 답변:

이 영상 해법은 위 문제에 도움이 된다고 튜터들이 추천한 것입니다.

영상 길이:

주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Infrared Spectroscopy

Infrared spectroscopy is a technique used to identify molecular structures by measuring the absorption of infrared light, which causes molecular vibrations. Different functional groups absorb light at characteristic wavenumbers, allowing for the identification of specific bonds, such as O-H stretches in alcohols.

Hydrogen Bonding

Hydrogen bonding occurs when a hydrogen atom covalently bonded to a highly electronegative atom, like oxygen, interacts with another electronegative atom. In ethanol, hydrogen bonding can affect the O-H stretch frequency; stronger hydrogen bonding typically results in a lower wavenumber due to increased bond strength and reduced vibrational frequency.

Solvent Effects

The choice of solvent can significantly influence the vibrational frequencies observed in infrared spectroscopy. In non-polar solvents like carbon disulfide, ethanol's hydrogen bonding interactions are diminished, potentially leading to a higher wavenumber for the O-H stretch compared to undiluted ethanol, where strong intermolecular hydrogen bonds are present.