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Select the vibrations that should be infrared active.
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Select the vibrations that should be infrared active.
- CH3CH2C = CCH2CH3 (C = C stretch)
- (CH3)2C = O (C = O stretch)
- trans – 4 – octane (C = C stretch)
- (CH3CH2)3C – CI (C – CI stretch)
- CH3CH2CH2C = CH (C = C stretch)
IR active molecules include molecules that are able to take in IR vibrations more powerfully than other molecules. If a molecule is IR activated, it must possess a dipole moment. The homoatomic molecules can be described as IR inactive since they have zero dipole moment , whereas heteroatomic compounds are IR active in the natural.♦ Relevant knowledgeIR Active Molecules
The vibration spectrum is the spectrum that occurs from the transition between the vibrationalenergy levels in a molecule. These spectra are found in the spectral range 4000-500 cm -1. Compounds with a permanent dipole moment are considered IR active.
The main criteria for molecules showing an infrared spectrum are that their dipole moment must change during vibration.
Permanent dipole moment molecules are IR inactive.
* [katex]{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{C}}{{\rm{H}}_{\rm{2}}}{\rm{C}} \equiv {\rm{CC}}{{\rm{H}}_{\rm{2}}}{\rm{C}}{{\rm{H}}_{\rm{3}}}[/katex]
This molecule is symmetric, and therefore does not have a dipole moment.
* [katex]{\left( {{\rm{C}}{{\rm{H}}_{\rm{3}}}} \right)_{\rm{2}}}{\rm{C = O\;\;}}[/katex]
This compound is an asymmetric one, and it has dipole moment.
* [katex]{\rm{trans – 4 – octene}}\,[/katex]
This compound is symmetric and has zero dipole moment.
* [katex]{\left( {{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{C}}{{\rm{H}}_{\rm{2}}}} \right)_{\rm{3}}}{\rm{C — CI\;\;\;}}[/katex]
This compound is asymmetric and shows dipole moment.
* [katex]{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{C}}{{\rm{H}}_{\rm{2}}}{\rm{C}}{{\rm{H}}_{\rm{2}}}{\rm{C = CH\;\;\;\;}}[/katex]
Because it is not symmetric, this compound has dipole moment.
IR active compounds
IR inactive compounds
[katex]{\left( {{\rm{C}}{{\rm{H}}_{\rm{3}}}} \right)_{\rm{2}}}{\rm{C = O\;\;}}\left( {{\rm{C = O stretch}}} \right)[/katex]
[katex]{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{C}}{{\rm{H}}_{\rm{2}}}{\rm{C}} \equiv {\rm{CC}}{{\rm{H}}_{\rm{2}}}{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{(C}} \equiv {\rm{C stretch)}}[/katex]
[katex]{\left( {{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{C}}{{\rm{H}}_{\rm{2}}}} \right)_{\rm{3}}}{\rm{C — CI\;\;\;}}\left( {{\rm{C – Cl stretch}}} \right)[/katex]
[katex]{\rm{trans – 4 – octene}}\,{\rm{(C = C}}\,{\rm{stretch)}}[/katex]
[katex]{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{C}}{{\rm{H}}_{\rm{2}}}{\rm{C}}{{\rm{H}}_{\rm{2}}}{\rm{C = CH\;\;\;\;}}\left( {{\rm{C = C stretch}}} \right)[/katex]
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