Study Set Content:
TYPES OF TRANSITIONS
- σ ⇾ σ* Transition
- n⇾ σ* transition
- n ⇾ π* & π π* transitions
An electron in a bonding σ orbital of a molecule is excited to the corresponding anti-bonding orbital by the absorption of radiation
sigma to sigma star transition
To induce a σ ⇾ σσ* transition it required
LARGE ENERGY
contains only single C-H bonds it undergoes only σ ⇾ σσ* transition only, it gives absorption maximum at 125nm
Methane
In this type of saturated compounds containing atoms with unshared electron pairs are undergo n ⇾ σσ* transition.
n to sigma star transition
It requires ____ energy than the σ ⇾ σσ* type
less
Most of the absorption peaks appear below
200nm
In the presence of polar solvents, the absorption maximum tends to shift () wavelength (Water, ethanol.)
shorter
In this the peaks in UV region are relatively small. (Methyl chloride, Oxygen, Nitrogen)
n to sigma star transition
n to pi star transition & pi to pi star transition
Most ____ undergo transitions for n ⇾ ππ* and π ⇾ ππ* transition.
Because energies required for processes bring the absorption peaks into spectral region.
organic compounds
Both transition require the presence of an ____ to the ´´Π´
orbitals.
unsaturated functional group
For π ⇾ ππ* ⧐
Alkenes, carbonyl compounds, alkynes
For n ⇾ ππ* ⧐
carbonyl compounds.
LAWS GOVERNING SPECTROMETRY
- BEER LAW
- LAMBERT LAW
- BEER-LAMBERT LAW
The intensity of a beam of monochromatic light decreases exponentially with increase in concentration of absorbing substance. But the law is applicable to dilute solutions only.
BEER LAW
When a beam of light passes through a transparent medium, the rate of decrease in intensity with thickness of medium is directly proportional to the intensity of light. The degree of the interactions is dependent on the contraction, there is a deviation from the linear relationship between contraction and absorbance.
LAMBERT LAW
is the linear relationship between absorbance and concentration of an absorbing species.
Beer-Lambert law (or Beer's law)
The general Beer-Lambert law is usually written as:
A = a(λλ) x b x c
is the measured absorbance
A
is a wavelength-dependent absorptivity coefficient,
a(λλ)
