Organic Spectroscopy

What spectroscopy must be used when the molecular formula is not known?

mass spectrometry

Infrared is absorbed by molecules causing them to

move to excited vibrational states

What is an IR spectrum useful for?

determining presence of functional groups

What is the difference between wavenumber and frequency?

the speed of light (1/lambda vs c/lambda)

What are the units of wavenumbers

cm^-1

what are the axes of IR plots

x = wavenumber/wavelength y=%transmission

What is the approximate frequency of an O-H or N-H stretch

3400 cm^-1

What is the approximate frequency of an C-H (sp³) stretch

3000-2850 cm^-1

What is the approximate frequency of an C-H (sp²) stretch

3100-3000 cm^-1

What is the approximate frequency of an C-H (sp) stretch

3300

What is the approximate frequency of a C≡C and C≡N stretch

2100 cm^-1

What is the approximate frequency of a C=O

1700 cm^-1

What is the approximate frequency of a C=C, aromatic C-C

1600 cm^-1

What is the approximate frequency of a aromatic C-C

1500 cm^-1

When a nuclei has magnetic moment, in a strong magnetic field it will

absorb electromagnetic radiation in the radio frequency range

¹H NMR spectra, given the integration of areas under signals in a spectrum provides

relative number of equivalent protons producing each signal

What is the n+1 rule?

if a proton is coupled to neighboring protons it will split into n+1 peaks

What is the chemical shift for an H attached to a sp³ C

1 ppm

What is the chemical shift for an H attached to a C atom attached to a pi-system

2 ppm

What is the chemical shift for an H attached to a C atom attached to an O atom

3-4 ppm

What is the chemical shift for an H attached to an sp² C atom

5-6 ppm

What is the chemical shift for an H attached to an aromatic C atom

7-8 ppm

What is the chemical shift for an H attached to an aldehyde C atom

10 ppm

What is the chemical shift for an H attached to a carboxylic acid C atom

11-12 ppm

the number of lines in a ¹³C spectra correspond to what

number of different types of carbon atoms in a molecule

What is the chemical shift for an sp³ alkyl C atom

10-30 ppm

What is the chemical shift for an sp³ C atom attached to an O, N, or X

50-70 ppm

What is the chemical shift for an sp C atom

75-90 ppm

What is the chemical shift for an sp² C atom

100-150 ppm

What is the chemical shift for an ester, amide, carboxyl C=O

160-180 ppm

What is the chemical shift for an aldehyde and ketone C=O

190-200 ppm

Measuring ion deflections yields a mass spectrum where ions are arranged according to

mass to charge (m/z) ratio

Molecular ions have the same mass as

the molecule

Molecular ions often fragment into

smaller ions and neutral components (radicals)

Fragmentation patters provide clues as to

structure of molecule

Abundances of fragment ions reflect

carbocation and radical stabilities

Resonance introduces single bonded character and therefore

reduces wavenumber signal

the carbonyl band for amides lies around

1650 cm^-1

bonding to electronegative atoms with a max seperation of 2 atoms will shift the NMR signal

downfield

resonance will increase electron density therefore shifting the NMR signal

upfield

increasing substitution shifts NMR signal

downfield

What is the significance of electron density with regard to chemical shift?

electron density results in shielding/deshielding effects, so different protons present in different ranges of chemical shifts

Why does bonding to an electronegative atom increase chemical shift?

electronegative atoms decrease electron density on the proton leading to deshielding

chemical shift of an amine

1-5 ppm

chemical shift of an alcohol

1-5.5 ppm

chemical shift of a carbonyl

2-2.7 ppm

chemical shift of an ether

3-3.4 ppm

chemical shift of an alkene

4.5-7.5 ppm

chemical shift of an aromatic proton

6-9 ppm

chemical shift of an aldehydic proton

9-10 ppm

If there is symmetry in the molecule, this implies what about the protons?

there will be equivalent protons with the same signal

the peak at 0 ppm on a proton nmr spectra is BLANK to analyzed molecule, and is representative of BLANK

not relevant, reference compound tetramethylsilane

what would be the multiplicity of proton a

quartet

what would be the mutliplicity of proton b

doublet

what would be the mutliplicity of proton a

triplet

what would be the multiplicity of proton b

doublet

Resonance involving a carbonyl group moves the chemical shift

downfield (increased)

The most likely major fragment of a molecule will also be the

most stable carbocation

The major fragmentation of the molecular ion of ketones is

either alkyl group attached to carbonyl carbon atom to be lost as an alkyl radical to generate corresponding acyl cation

what the major type of fragmentation for alcohols, amines, and all types of carbonyl compounds?

alpha-cleavage

quaternary carbons produce BLANK in C NMR spectra

low signals

IR freq of terminal alkynes

3330-3270 cm^-1

IR freq of aldehydes

2830-2695 cm^-1

IR freq of nitriles

2260-2210 cm^-1

IR freq of non-terminal alkynes

2260-2100 cm^-1

IR freq of alkenes

1680-1640 cm^-1

IR frequency of C-O stretch of alcohols, carboxylic acids, esters, and ethers

1320-1000 cm^-1

IR freq of O-H bend of carboxylic acids

950-910 cm^-1

IR freq of n-H bend of primary amines

1650-1580 cm^-1