IB Chemistry Topic S3.2.9 Infrared Spectra Revision Notes (HL)

IB Chemistry Topic S3.2.9 Infrared Spectra Revision Notes (HL) | RevisionDojo

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How IR Spectroscopy Works

Analogy

Consider the bonds between atoms in a molecule as tiny springs connecting weights.
These "springs" can stretch, compress, and bend when they absorb energy.
Infrared radiation provides just the right amount of energy to make these bonds vibrate at specific frequencies.

What Determines Vibration Frequencies?

Two main factors influence how a bond vibrates:
1. Bond Strength: Stronger bonds (like $C \equiv C$ triple bonds) vibrate at higher frequencies, while weaker bonds (like $C–C$ single bonds) vibrate at lower frequencies.
2. Atomic Masses: Lighter atoms vibrate at higher frequencies compared to heavier ones.
When a molecule absorbs infrared radiation, it produces an IR spectrum, a graph of absorbance or percent transmittance at different wavenumbers (measured in cm⁻¹).
The wavenumber is inversely related to the wavelength of the absorbed radiation.

Interpreting the Functional Group Region of an IR Spectrum

The IR spectrum can be divided into two regions:

Functional Group Region (4000–1500 cm⁻¹): This region contains peaks that correspond to specific functional groups, making it the most useful for identification.
Fingerprint Region (1500–400 cm⁻¹): This region is unique to each molecule and is often used for comparison rather than identifying functional groups.

Key Functional Group Absorptions

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How IR Spectroscopy Works

Analogy

Consider the bonds between atoms in a molecule as tiny springs connecting weights.
These "springs" can stretch, compress, and bend when they absorb energy.
Infrared radiation provides just the right amount of energy to make these bonds vibrate at specific frequencies.

What Determines Vibration Frequencies?

Two main factors influence how a bond vibrates:
1. Bond Strength: Stronger bonds (like $C \equiv C$ triple bonds) vibrate at higher frequencies, while weaker bonds (like $C–C$ single bonds) vibrate at lower frequencies.
2. Atomic Masses: Lighter atoms vibrate at higher frequencies compared to heavier ones.
When a molecule absorbs infrared radiation, it produces an IR spectrum, a graph of absorbance or percent transmittance at different wavenumbers (measured in cm⁻¹).
The wavenumber is inversely related to the wavelength of the absorbed radiation.

Interpreting the Functional Group Region of an IR Spectrum

The IR spectrum can be divided into two regions:

Functional Group Region (4000–1500 cm⁻¹): This region contains peaks that correspond to specific functional groups, making it the most useful for identification.
Fingerprint Region (1500–400 cm⁻¹): This region is unique to each molecule and is often used for comparison rather than identifying functional groups.

Key Functional Group Absorptions

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Structure 1. Models of the particulate nature of matter5 subtopics

Structure 2. Models of bonding and structure4 subtopics

Structure 3. Classification of matter2 subtopics

Reactivity 1. What drives chemical reactions?4 subtopics

Reactivity 2. How much, how fast and how far?3 subtopics

Reactivity 3. What are the mechanisms of chemical change?4 subtopics

IB Chemistry S3.2.9 Infrared Spectra Notes

How IR Spectroscopy Works

What Determines Vibration Frequencies?

Interpreting the Functional Group Region of an IR Spectrum

Key Functional Group Absorptions

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Duis aute irure dolor in reprehenderit

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Unlock the rest of this chapter with a free account

How IR Spectroscopy Works

What Determines Vibration Frequencies?

Interpreting the Functional Group Region of an IR Spectrum

Key Functional Group Absorptions

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account

Structure 1. Models of the particulate nature of matter5 subtopics

Structure 2. Models of bonding and structure4 subtopics

Structure 3. Classification of matter2 subtopics

Reactivity 1. What drives chemical reactions?4 subtopics

Reactivity 2. How much, how fast and how far?3 subtopics

Reactivity 3. What are the mechanisms of chemical change?4 subtopics