•__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
•__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.
c = λv
speed of light
•__ 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.
The IR region
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 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?
isolated C=C (1640-1680)
conjugated C=C (1620-1640)
aromatic C=C (1600)
Carbon Hydrogen bond stretches
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, __.
•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 __ . =>
below 2200 cm-1
The absence of a signal is definite proof of what?