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MCAT Org. Chem Ch.11

QuestionAnswer
Infrared (IR) Spectroscopy Measures: Absorption of infrared light which causes molecular vibration (stretching, bending, twisting, and folding)
IR Spectra Are Generally Plotted As: Percent transmittance vs. wavenumber (1 / λ)
Normal Range Of An IR Spectra: 4000 to 400 cm^-1
Fingerprint Region Of An IR Spectra: Between 1500 and 400 cm^-1. This contains a number of peaks that can be used by experts to identify a compound.
To Appear On An IR Spectrum, Vibration Of A Bond Must change: The bond dipole moment.
Certain Bonds Have Characteristic: Absorption frequencies which allow us to infer the presence or absence of particular functional groups
O-H Peak Is A: Broad peak around 3300 cm^-1. Molecules with O-H include alcohols, water, and carboxylic acids.
The Carboxylic Acid O-H Peak Will Be Around: 3000 cm^-1.
N-H Peak Is A: Sharp peak around 3300 cm^-1. Molecules with N-H include some amines, imines, and amides.
C=O Peak Is A: Sharp peak around 1750 cm^-1. Molecules with C=O include aldehydes, ketones, carboxylic acids, amides, esters, and anhydrides.
Ultraviolet (UV) Spectroscopy Measures: Absorption of ultraviolet light which causes movement of electrons between molecular orbitals
UV Spectra Are Generally Plotted As: Percent transmittance or absorbance vs. wavelength
To Appear On A UV Spectrum, A Molecule Must Have A Small Enough Energy Difference Between Its: Highest occupied molecular orbital (HOMO) and its lowest unoccupied molecular orbital (LUMO) to permit an electron to move from one orbital to the other.
The Smaller The Difference Between HOMO And LUMO: The longer the wavelengths a molecule can absorb
Conjugation Occurs In Molecules With: Unhybridized p-orbitals.
Conjugation Shifts The Absorption Spectrum To: Higher maximum wavelengths (lower frequencies)
Nuclear Magnetic Resonance (NMR) Spectroscopy Measures: Alignment of nuclear spin with an applied magnetic field which depends on the magnetic environment of the nucleus itself.
NMR Is Useful For: Determining the structure (connectivity) of a compound, including the functional groups
Nuclei May Be In The Lower-Energy α-State Or Higher-Energy β-State In Which: Radiofrequency pulses push the nucleus from the α-state to the β-state and these frequencies can be measured
Magnetic Resonance Imaging Is A: Medical application of NMR spectroscopy
NMR Spectra Are Generally Plotted As: Frequency vs. absorption of energy.
NMR Spectra Are Standardized By Using: Chemical shift (δ), which is measured in parts per million (ppm) of spectrophotometer frequency.
NMR Spectra Are Calibrated Using: Tetramethylsilane (TMS) which has a chemical shift of 0 ppm
Higher Chemical Shifts In NMR Are Located To The: Left (downfield)
Lower Chemical Shifts In NMR Are Located To The: Right (upfield)
Each Unique Group Of Protons In Proton (1H) NMR: Has its own peak
Integration (Area Under The Curve) Of Each Proton (1H) NMR Peak Is proportional to the number of protons contained under the peak
Deshielding Of Protons Occurs When: Electron-withdrawing groups pulls electron density away from the nucleus which allows it to be more easily affected by the magnetic field.
Deshielding Moves A Peak: Further downfield.
When Hydrogens Are On Adjacent Atoms, They: Interfere with each other's magnetic environment, which causes spin-spin coupling (splitting)
A Proton's Or Group Of Protons' Peak Is Split Into: n+1 subpeaks, where n is the number of protons that are three bonds away from the proton of interest.
Splitting Patterns Include: Doublets, triplets, and multiplets
Protons On Sp3-hybridized Carbons Are Usually In The: 0 to 3 ppm range (but higher if electron-withdrawing groups are present)
Protons On Sp2-hybridized Carbons Are Usually In The: 4.6 to 6.0 ppm range
Protons On Sp-hybridized Carbons Are Usually In The: 2.0 to 3.0 ppm range
Aldehydic Hydrogens Tend To Appear: Between 9 to 10 ppm
Carboxylic Acid Hydrogens Tend To Appear: Between 10.5 and 12 ppm
Aromatic Hydrogens Tend To Appear: Between 6.0 and 8.5 ppm
Created by: SamB91