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•__is an analytical technique which helps determine structure.
•It destroys little or no sample.
The amount of light absorbed by the sample is measured as __is varied.
•__ measures the bond vibration frequencies in a molecule and is used to determine the functional group.
•__ fragments the molecule and measures the masses.
- Infrared (IR) spectroscopy
- Mass spectrometry
•__spectroscopy detects signals from hydrogen atoms and can be used to distinguish isomers.
•__ uses electron transitions to determine bonding patterns. =>
- Nuclear magnetic resonance (NMR)
- Ultraviolet (UV) spectroscopy
•__, where c is the __.
Energy per photon = __, where h is Planck’s constant.
•__ is just below red in the visible region.
•Wavelengths usually 2.5-25 mm.
•More common units are __, or cm-1, the reciprocal of the wavelength in centimeters.
Wavenumbers are proportional to frequency and energy.
If stretched,, where is the spring force?
if compressed, where?
- spring force is in
- spring force is out
Frequency decreases with __.
Frequency increases with __.
- increasing AW
- increasing bond energy
•__ are also quantitized.
•No two molecules will give exactly the same __
•Simple stretching: 1600-3500 cm-1.
Complex vibrations: 600-1400 cm-1, called the “__region.”
- Whole-molecule vibrations and bending vibrations
- IR spectrum (except enantiomers).
•A polar bond is usually __.
•A nonpolar bond in a symmetrical molecule will absorb __.
- weakly or not at all.
What are the C-C bond frequencies?
- C-C (1200)
- C=C (1660)
- C***C (2200)
- isolated C=C (1640-1680)
- conjugated C=C (1620-1640)
- aromatic C=C (1600)
Carbon Hydrogen bond stretches
- C-H 2800-3000
- =C-H 3000-3100
- ***C-H 3300
Both OH and NH occur around __, but what's the differences.
- Alcohol OH is broad with a rounded tip
- Secondary amine is broad with one sharp spike
- Primary amine is broad with two sharp spikes
- no signal for tertiary
The C=O bond of simple ketones, ald., and carb acids absorb around __.
Usually, its the __.
__ will also have OH.
__ have two CH signals around __.
strongest IR signal
2700 and 2800 cm-1
•Conjugation of C=O with C=C lowers the stretching frequency to ~__cm-1.
•The C=O group of an __absorbs at an even lower frequency, __.
- 1640-1680 cm-1
•The C=O of an __absorbs at a higher frequency, ~__cm-1.
Carbonyl groups in __absorb at an even higher frequency
small rings (5 C’s orless)
C-N absorbs around __
C=N absorbs around __ and is much stronger than the __ in teh same region.
C *** N absorbs strongly just __. The alkyne C C signal is much weaker and is just __ . =>
- 1200 cm
- above 2200
- below 2200
- below 2200 cm-1
The absence of a signal is definite proof of what?
that the functional group is absent