Ultraviolet and Infrared Spectroscopy Flashcards
What is required for absorption of electromagnetic radiation to occur in a molecule?
The energy of the photon must match the difference between two energy states in the molecule (ground state to excited state)
The larger the energy difference between two states-
the higher the energy of radiation needed for absorption
Higher energy light (UV-visible) causes
electronic excitation
Lower energy radiation (infrared) causes
vibrational excitation
What bonds absorb at a wavelength of between 4000-2500
Bonds to hydrogen (C-H, O-H, N-H)
What bonds absorb at a wavelength of 2500-2000
Triple bonds
What bonds absorb at a wavelength of 2000-1500
Double bonds
What bonds absorb at a wavelength of 1500-400
Single bonds
The higher the percent s-character-
the stronger the bond and the higher the wavelength of absorption
What bonds in the IR spectrum absorb at around 3000-2850 cm-1
Csp3-H bonds (alkane)
What bonds absorb at 3150-3000 cm-1
Csp2-H bonds (alkene, double bond)
What bonds absorb at 3300 cm-1
Csp-H bonds (alkyne, triple bond)
What compounds absorb at 1600, 1500
Benzene
What molecules absorb at 3600-3300
Alcohols
What molecules absorb at 3500 - 3300
Amine, N-H
What bonds absorb at 2830-2700 IR
Aldehydes (Csp2-H)
What functional group absorbs at 1730 IR
Aldehyde (C double bond O)
What functional group absorbs at 1715 IR
Ketone (C double bond O)
What functional group absorbs at 1745 - 1735
Ester (C doulbe bond O)
What functional group absorbs at 1680-1630 IR
Amide (C double bond O) (N-H at 3400 - 3200)
What functional group aborbs at 3500-2500 (O-H) and 1710 (CdoublebondO)
Carboxylic acid
What functional group absorbs at 2250
Nitrile (ctriple bondN)
What are the two main uses of UV Spectroscopy
Measure at one wavelength and record full spectrumm
The Beer-Lambert Law to calculate the relationship for the fraction of light absorbed on passage through a solution
log10(IncI/EmeI) = e x c x length = A
(IncI = Incident light intensity) (EmeI = emergent light intensity) (e = molar decadic extinction coefficient)
