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MCAT Org. Chem Ch.11
| Question | Answer |
|---|---|
| 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
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