Spectroscopy Flashcards
measures the energy differences between the possible states of a molecular system by determining the frequencies of electromagnetic radiation absorbed by the molecules; types include infrared, ultraviolet, and nuclear magnetic resonance (NMR)
spectroscopy
measures absorption of ____ light, which causes molecular vibration (can be seen as bond stretching, bending, twisting, and folding)
infrared (IR) spectroscopy
infrared (IR) spectroscopy:
general plot of IR spectrum
percent transmittance vs wavenumber (1/λ)
infrared (IR) spectroscopy:
normal range of IR spectrum
4000 to 400 cm^-1
infrared (IR) spectroscopy:
between 1500 and 400 cm^-1; contains a number of peaks that can be used to identify a compound
fingerprint region
infrared (IR) spectroscopy:
must be changed by the vibration of a bond to appear on an IR spectrum
bond dipole moment
infrared (IR) spectroscopy:
have characteristic absorption frequencies, which allow us to infer the presence (or absence) of particular functional groups
specific bonds
infrared (IR) spectroscopy:
a broad peak around 3300 cm^-1
O-H peak
infrared (IR) spectroscopy:
a sharp peak around 3300 cm^-1
N-H peak
infrared (IR) spectroscopy:
a sharp peak around 1750 cm^-1
C=O peak
measures absorption of ____ light, which causes movement of electrons between molecular orbitals
ultraviolet (UV) spectroscopy
ultraviolet (UV) spectroscopy:
general plot of UV spectrum
percent transmittance or absorbance vs wavelength
ultraviolet (UV) spectroscopy:
must be small enough to permit an electron to move from one orbital to the other to appear on a UV spectrum
energy difference between HOMO and LUMO
ultraviolet (UV) spectroscopy:
shifts the absorption spectrum to higher maximum wavelengths (lower frequencies)
conjugation
measures alignment of nuclear spin with an applied magnetic field, which depends on the magnetic environment of the nucleus itself; useful for determining the structure (connectivity) of a compound, including functional groups
nuclear magnetic resonance (NMR) spectroscopy
nuclear magnetic resonance (NMR) spectroscopy:
push the nucleus from the α-state to the β-state, and these frequencies can be measured
radiofrequency pulses
nuclear magnetic resonance (NMR) spectroscopy:
low-energy state
α-state
nuclear magnetic resonance (NMR) spectroscopy:
high-energy state
β-state
nuclear magnetic resonance (NMR) spectroscopy:
a medical application of NMR spectroscopy
magnetic resonance imaging (MRI)
nuclear magnetic resonance (NMR) spectroscopy:
general plot of NMR spectrum
frequency vs absorption of energy
nuclear magnetic resonance (NMR) spectroscopy:
standardizes plot of NMR spectra, measured in parts per million (ppm) of spectophotometer frequency
chemical shift (δ)
nuclear magnetic resonance (NMR) spectroscopy:
used to calibrate NMR, has a chemical shift of 0 ppm
tetramethylsilane (TMS)
nuclear magnetic resonance (NMR) spectroscopy:
to the left in a NMR spectrum, where higher chemical shifts are found
downfield
nuclear magnetic resonance (NMR) spectroscopy:
to the right on a NMR spectrum, where lower chemical shifts are found
upfield
nuclear magnetic resonance (NMR) spectroscopy:
the most common type of NMR; each unique group of protons (-H) have their own peak
proton (^1H) NMR
proton (^1H) NMR:
area under the curve of a peak, is proportional to the number of protons represented by the peak
integration
proton (^1H) NMR:
occurs to protons when electron-withdrawing groups pull electron density away from the nucleus, allowing it to be more easily affected by the magnetic field; moves a peak further downfield
deshiedling
proton (^1H) NMR:
caused when hydrogens are on adjacent atoms and they interfere with each other’s magnetic environment; a proton’s (or group of proton’s) peak is ____ into n+1 subpeaks, where n is the number of protons that are three bonds away from the proton of interest
splitting (spin-spin coupling)
proton (^1H) NMR:
include doublets, triplets, and multiplets
splitting patterns
proton (^1H) NMR:
shift from 0 to 3 ppm
alkyl groups
proton (^1H) NMR:
shift from 2 to 3 ppm
alkynes
proton (^1H) NMR:
shift from 4.6 to 6 ppm
alkenes
proton (^1H) NMR:
shift from 6 to 8.5 ppm
aromatics
proton (^1H) NMR:
shift from 9 to 10 ppm
aldehydes
proton (^1H) NMR:
shift from 10.5 to 12 ppm
carboxylic acids
