Does anyone have any INFRARED SPECTROSCOPY notes?

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foxstudy
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^^^^
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mnnbv
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check chemguide, they have pdf notes for all topics
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charco
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(Original post by foxstudy)
^^^^
What do you want to know?

Covalent molecules can absorb IR radiation and use it to change the vibrational states of its bonds. There are three types of vibration.
1. symmetric stretch
2. asymmetric stretch
3. bend
Provided the vibrational state change is accompanied by a change in the dipole moment then it is IR active (shows up as IR absorption)

The sample is held between two ionic discs (potassium chloride) which are transparent to IR radiation.

An IR spectrum is recorded by sweeping across a range of electromagnetic radiation in the IR region and the absorbance of the sample is compared to the absorbance of a reference (usually nothing, or a hydrocarbon solvent, eg nujol).

The actual spectrum of absorbances is usually very complex and not much useful information is obtained. However, certain groups of atoms give characteristic absorptions that can be identified by reference to a data table.

If there is a database of IR spectra then the sample can be compared to known compounds and identified by its "fingerprint"
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foxstudy
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(Original post by charco)
What do you want to know?

Covalent molecules can absorb IR radiation and use it to change the vibrational states of its bonds. There are three types of vibration.
1. symmetric stretch
2. asymmetric stretch
3. bend
Provided the vibrational state change is accompanied by a change in the dipole moment then it is IR active (shows up as IR absorption)

The sample is held between two ionic discs (potassium chloride) which are transparent to IR radiation.

An IR spectrum is recorded by sweeping across a range of electromagnetic radiation in the IR region and the absorbance of the sample is compared to the absorbance of a reference (usually nothing, or a hydrocarbon solvent, eg nujol).

The actual spectrum of absorbances is usually very complex and not much useful information is obtained. However, certain groups of atoms give characteristic absorptions that can be identified by reference to a data table.

If there is a database of IR spectra then the sample can be compared to known compounds and identified by its "fingerprint"
This is my current knowledge. Also I'm on the WJEC exam board so I don't need to know about the different ways the bonds can vibrate but thanks anyway.

Infrared spectroscopy helps us identify the functional groups in an unknown compound.

The method is:
- infrared radiation is passed through a sample
- the bonds in the molecules of the sample absorb the infrared radiation
- this causes the bonds to vibrate <--- edit: vibrate MORE

I don't understand what the term wavenumber means and what the bonds actually absorb (absorption of certain frequencies/energies/wavelength of infrared radiation??- like I never know which term to use in the context)
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charco
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(Original post by foxstudy)
This is my current knowledge. Also I'm on the WJEC exam board so I don't need to know about the different ways the bonds can vibrate but thanks anyway.

Infrared spectroscopy helps us identify the functional groups in an unknown compound.

The method is:
- infrared radiation is passed through a sample
- the bonds in the molecules of the sample absorb the infrared radiation
- this causes the bonds to vibrate <--- edit: vibrate MORE

I don't understand what the term wavenumber means and what the bonds actually absorb (absorption of certain frequencies/energies/wavelength of infrared radiation??- like I never know which term to use in the context)
Wavenumber is another way of decribing the electromagnetic energy. It is equal to the reciprocal of the wavelength in centimetres.

As:

E = hc/λ

and h and c are constants, λ is the wavelength.

Then E is proportional to the reciprocal of λ

The bonds absorb the electromagnetic energy and use it to increase the quantum energy level of the vibrational states (described above)
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Chemist123
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Is this gcse or A level?
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foxstudy
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(Original post by Chemist123)
Is this gcse or A level?
A level
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foxstudy
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(Original post by charco)
Wavenumber is another way of decribing the electromagnetic energy. It is equal to the reciprocal of the wavelength in centimetres.

As:

E = hc/λ

and h and c are constants, λ is the wavelength.

Then E is proportional to the reciprocal of λ

The bonds absorb the electromagnetic energy and use it to increase the quantum energy level of the vibrational states (described above)
so the bonds absorb infrared energy which causes them to vibrate more and the wavenumber range is the amount of energy absorbed by the bonds?

is infrared energy the correct term or frequency of the infrared radiation?
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charco
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(Original post by foxstudy)
so the bonds absorb infrared energy which causes them to vibrate more and the wavenumber range is the amount of energy absorbed by the bonds?

is infrared energy the correct term or frequency of the infrared radiation?
the frequency is directly proportional to the energy, as E = hf, and h is constant.
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foxstudy
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(Original post by charco)
the frequency is directly proportional to the energy, as E = hf, and h is constant.
So because they're directly proportional they're interchangeable?
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