NMR

Question 1

• What is the number of carbon environments?

Answer 1

• In any organic molecule, the different carbon atoms are not necessarily equivalent to each other
• This is because they can have different amounts of electron density around each atom
• The electron density AROUND A CARBON is determined by its proximity TO other carbons, electronegative atoms, or functional groups
• Each carbon which has a different amount of electron density around it is said to be in a different environment

Question 2

• How many carbon environments? (Ethanol)

Answer 2

• Ethanol has 2 different carbon environments
• Carbon 2 is bonded directly to an oxygen and will have a slightly lower electron density than carbon 1

Question 3

• How many carbon environments? (Propan-1-ol)

Answer 3

• Propan-1-ol has 3 different carbon environments
• Carbon 3 is bonded to an oxygen and will have a lower electron density
• Carbon 2 is bonded to 2 carbons, and carbon 1 is only bonded to one other carbon
• As such they are all in different carbon environments

Question 4

• How many carbon environments? (Ethylethanoate)

Answer 4

• Ethylethanoate has 4 different carbon atoms, and each are in their own environment

Question 5

• How many carbon environments? (Butane)

Answer 5

• Butane has 4 carbon atoms, but 2 different carbon environments
• The 2 on either end of the molecule are in one environment, and the 2 in the centre are in a different environment

Question 6

• What is Tetra Methyl Silane?

Answer 6

• TMS is used as a reference standard for chemical shifts
• A few drops of TMS are added to the compound to be analysed by the spectrometer
• All peaks generated by the sample have a chemical shifts relative to the peak caused by TMS at 0ppm

Question 7

• Why is TMS used as a standard?

Answer 7

• It generates one sharp peak
• It is unreactive so won’t affect the sample being analysed
• It is highly volatile, this means it can be removed from the sample being tested after the analysis fairly easily
• Peak always found on the far right of the spectrum

Question 8

• What is the molecular formula of TMS?

Answer 8

• C4H12Si