organic chemistry: 11: Spectroscopy

[... spectroscopy] measures absorption of infrared light, which causes molecular vibration such as stretching, bending, twisting, and folding

infrared spectroscopy

• based on this it is possible to determine the functional groups that make up the molecule

• plotted as % transmittance vs. wavenumber (1/wavelength sign)

The IR spectroscopy frequency for N-H bonds is [...] cm^-1

N0H bond is 3300

The IR spectroscopy frequency range for O-H bonds is [...] - [...] cm^-1 

O-H bond is 3000-3300

The IR spectroscopy frequency range for CO and CN triple bonds is [...] - [...] cm^-1

CO and CN triple bond is 19000-2200

The IR spectroscopy frequency for C=O bonds is [...] cm^-1

C=O 1750

The IR spectroscopy frequency range for C=C bonds is [...] - [...] cm^-1 

C=C 1600-1680

The type of bond indicated in this IR spectroscopy chart is [...]

N-H

The types of bonds indicated in this IR spectroscopy chart are [...] and [...]

C-H and C=O

the types of bonds indicated in this IR spectroscopy chart are [...] and [...]

O-H and C-O

[... spectroscopy] measures the absorption of UV light, which causes movement of electrons between molecular orbitals

ultraviolet spectroscopy

uv spectra are plotted as percent transmittance or absorbance vs wavelength.

[... spectroscopy] measures alignment of nuclear spin with an applied magnetic field

nuclear magnetic resonance spectroscopy

-NMR spectroscopy is useful for determining the structure (connectivity) of a compound, including functional groups

plotted as frequency vs. absorption energy

NMR spectra are calibrated using [...], which has a chemical shift of 0 ppm

calibrated

The [...] is the area under each peak (signal) on the NMR spectrum. It corresponds to the number of protons in that signal

integration

[...] in NMR spectroscopy is when a nucleus' chemical shift is increased due to the removal of electron density, magnetic induction, or other effects

deshielding

• deshielding is the opposite of shielding

In NMR spectroscopy, the [...] is the position on the δ scale (in ppm) where the peak occurs

chemical shift

In NMR spectroscopy, a peak that is deshielded appears [downfield or upfield]

downfield (left)

In NMR spectroscopy, a peak that is shielded appears [downfield or upfield]

upfield (right)

When hydrogens are on adjacent atoms, they interfere with each other’s magnetic environment, causing [...] also known as [...]

spin-spin coupling also known as splitting

In NMR spectroscopy, the multiplicity of a proton or group of protons is given by the n+1 rule, where n = [...]

n=the number of protons on the adjacent (adjoining) carbon carbon atom (atoms)

The hydrogens of a/an [...] group have an NMR range of 0.7 - 1.9 ppm

alkyl

A/an [...] hydrogen has an NMR range of 2.5 - 3.0 ppm

alkynyl

The hydrogens of a/an [...] have an NMR range of 2.0 - 2.4 ppm

methyl ketone

[...] hydrogens have an NMR range of 4.5 - 6.5 ppm

vinylic

The hydrogens of a/an [...] group have an NMR range of 6.5 - 8.0 ppm

aryl

The hydrogens of a/an [...] group have an NMR range of 9.7 - 10.0 ppm

aldehyde

The hydrogens of a/an [...] group have an NMR range of approximately 11.0 - 12.0 ppm

carboxylic acid

A mass spectrometer ionizes atoms and molecules with a high-energy electron beam and then deflects the ions through a magnetic field based on the [...] of the ion

mass to charge ratio (m/z)

• the mass spectrum of a sample shows relative abundance of each ion on the y-axis and m/z along the x-axis

The largest peak in the mass spectrum, corresponding to the most abundant ion, is called the [...]

base peak

In the mass spectrum, the heaviest ion (the one with the greatest m/z value) is likely to be the [...]

molecular ion

In a mass spectrum, the [...] peak is a small peak 1 m/z unit to the right of the main molecular ion peak

m+1

• the M+1 peak shows the relative abundance of 13C

• 13C is found in relative abundance of 1.1%

• so, the M+1 has an m/z value of 4.4 that means there are 4 carbons single 4.4/1.1 = 4

In a mass spectrum, the M+2 peak shows the relative abundance of either [...] or [...]

81 Br and 37 Cl

Br: has a 1:1 ration relative to the M peak

Cl has a 3:1 ration relative to the M peak

In a mass spectrum:

Br has a [...] ratio relative to the M peak

Cl has a [...] ratio relative to the M peak

1:1

3:1

Based on the size of the M+2 peak, you know this is a mass spectrum of a molecule that contains [element]

bromine

• Br has a 1:1 ratio relative to the M peak

Based on the size of the M+2 peak, you know this is a mass spectrum of a molecule that contains [element]

chlorine

cl has a 3:1 ratio relative to the m peak