Principles Lab – High/Low Field instruments. 2. Carbon 13.

Take a C-13 spectrum of a neat (1-99) and solution (1-98) ethyl benzene on both the EFT 60 and the Unity Plus 500. For all of the spectra use ns=16 (or nt=16 on the unity plus). After the spectrum is obtained with the Unity plus; use the dsn command to calculate have the computer calculate the signal to ratio for your spectrum and you should write it down on the plot. After the spectrum is obtained with the EFT 60; use the sn command to calculate have the computer calculate the signal to ratio for your spectrum and you should write it down on the plot. Write up your results. In what ways are the spectra the same and have the same information. In what ways are they different.

For the 1-98 sample from the Unity Plus 500 calculate the signal to noise ratio yourself. The signal to noise values can be calculated manually by 1)measuring the height of peak, HS, (the distance from the top of the peak to the middle of the base line noise) 2) measuring the peak to peak height of the noise, HN (the total distance that includes all of the noise) 3) calculating the average noise, AV, by dividing the peak to peak noise by 2.5 (AV=HN/2.5).

The S/N ratio is then calculated as (HS/AV). Show your calculations. Does your calculated value agree approximately with the computer calculated value.

What is the signal to noise ratio in your C13 spectrum of sample 1-99 obtained with the EFT 60? Show your calculations?

1. Short answers.

On a 500 MHz instrument, 0.2 ppm in the proton spectrum corresponds to _______ Hz. On the same instrument, 0.2 ppm on the C-13 corresponds to __________ Hz.

¹³C has a spin of _____ and ____ orientations where as ²H has a spin of ____ and ____ orientations.

2. Consider the NMR of

3 methyl-2- butanone.

Draw the structure of the compound and label the different H’s in the compound using lower case letters starting with ‘a’.

Fill in the following table of these labeled protons with both the multiplicities of each and the integration. Leave blank any un-needed row. Fill in the integration of for each of these protons.

proton	Multiplicity Doublet, singlet, etc	Relative integration
a
b
c
d
e

3. Sketch the expected decoupled C-13 spectrum of 3 methyl-2- butanone. You will be graded on the number of peaks, approximate position of the peaks, rough intensity of the peaks, assignment of the peaks, and the labeling of the y axis.

4. Sketch the expected DEPT spectra (the kind you would get using the eft-60 instrument) of 3 methyl-2- butanone. You will be graded on the number of peaks, and assignment of the peaks.

5. Tell me as much as you can about the compound that gave the following proton spectrum. The relative integration of the peaks (from left to right) were experimental determined to be 49, 25, 26, 146.