UV/Vis and IR Spectroscopy Flashcards
spectrometry function
detects high energy fragments
spectroscopy function
detects light
absorption spectroscopy general process
1)light source
2) pass light through sample -> photon excites -> reaction
3)detector check for absorption
what does UV/Vis spectroscopy show you
electronic structure of molecule; conj pi systems
effect of conjugation on energy and absorbtion
more conj the pi system =
-lower energy photon (more stable the structure bc of resonance)
-smaller HOMO-LUMO gap
-increased wavelength (frequency of light decrease)
quantum leap
pi to pi* transition in conj pi systems; excited electron goes from ground state (HOMO) to LUMO
visible vs UV light range
the more conj the pi system, the larger the wavelength = the closer to the visible light range
goal of IR spectroscopy
detects vibration of bonds to determine bonds and functional groups present.
strength of bond and absorption frequency
the stronger the C-C/ C-H/ C-X bond the greater the absorption frequency = more intense signal
*C-X bonds; take into account electroneg of X atom
wavenumber range 3400-2800
O-H, N-H, C-H stretching; more intense signal can indicate hydrogen bonding
wavenumber range 2250-2100
C TRIPLE bond O, N, C stretching; more intense signal indicated asymmetry
wavenumber range 1850-1600
C DOUBLE bond C, O, N stretching; differentiation of carbonyl groups
wavenumbers under 1600
not super relevant; C-C, C-O, C-N, and C-H binding (1000-600)
differentiation of carbonyl containing compounds: ketone
- 1710 peak
- right of 3000 sp3 C-H signal
differentiation of carbonyl containing compounds: aldehyde
-1710 peak
- 2710 and 2810 (aldehyde sp2 C-H bond signal)
