Write-up procedure:

1. Determine molecular formula from elemental analysis.

2. Determine elements of unsaturation from molecular weight [EOU=1/2(2C+2-H)]

3. Show all work

4. Label important stretches in the NMR and IR

5. Determine the structure

Experiment 1 post lab due in two weeks(week of Feb 6th-10th)

Example 1:MW: 88.1; BP: 73-76 °C/12 mmHg(lit.), Elemental Composition: C 54.53% H 9.15%

Example 2:MW: 169.22; BP: 302 oC, MP 52-54 oC; Elemental Composition: C 85.17% H 6.55% N 8.28%

NMR Signals

• The number of signals shows how many different kinds of protons are present.

• The location of the signals shows how shielded or deshielded the proton is.

• The intensity of the signal shows the number of protons of that type.

• Signal splitting shows the number of protons on adjacent atoms.

The NMR Graph

Chapter 13 8

Tetramethylsilane

• TMS is added to the sample.• Since silicon is less electronegative

than carbon, TMS protons are highly shielded. Signal defined as zero.

• Organic protons absorb downfield (to the left) of the TMS signal.

=>

Si

CH3

CH3

CH3

H3C

Chapter 13 9

Chemical Shift

• Measured in parts per million.

• Ratio of shift downfield from TMS (Hz) to total spectrometer frequency (Hz).

• Same value for 60, 100, or 300 MHz machine.

• Called the delta scale. =>

Chapter 13 10

Delta Scale

=>

Chapter 13 11

Location of Signals

• More electronegative atoms deshield more and give larger shift values.

• Effect decreases with distance.

• Additional electronegative atoms cause increase in chemical shift. =>

Chapter 13 12

Typical Values

=>

C5H10O

Example 3:MW: 108.14; BP: 202 oC, MP 32-34 oC; Elemental Composition: C 77.75% H 7.46%

Example 4:MW: 108.14; BP: 203 oC, MP 8-10 oC; Elemental Composition: C 77.75% H 7.46%