Lab methods/ Spectroscopy Ochem

Question 1

Gas chromatography separates based on____?

Answer 1

Boiling pt/volatility
Lowest BP will elute first
Volatility= tendency of molecule to convert to gas
volatility is inversely proportional to IMF and BP

Question 2

Factors that affect BP

Answer 2

Molecular weight-heavier molecules have higher BP

Branching-more branching lowers BP

Question 3

What does BP measure?

Answer 3

BP measures 3 intermolecular forces

1) H bonds
2) Dipole-dipole
3) London dispersion

Question 4

Spin-spin coupling

Answer 4

Occurs between neighboring NON-EQUIVALENT sets of Hydrogens

Question 5

What type of molecules will have the largest Rf values when eluted with hexanes during TLC?

Answer 5

Nonpolar molecules will travel farther and therefore have larger Rf values. Polar molecules will be “interested” and spend more time on the TLC plate, hence will have a lower Rf value

Question 6

Triplet vs Quartet hydrogens

Answer 6

Remember n+1
If 3 hydrogens, e.g., on a methyl group, it will be 3+1=4, i.e. a quartet
If 2 hydrogens, e.g., CH2, 2+1=3, i.e. a triplet

Question 7

What is spectroscopy used for?

Answer 7

compound identification

Distillation, crystallization, extraction are used to separate and purify

Question 8

Distillation separates based on_____

Answer 8

Boiling point

Therefore, Distillation would be good technique to separate nonane from acetone

Question 9

When pH > pI, what happens to amino acid?

Answer 9

amino acid will be deprotonated, therefore will have an overall negative charge

Question 10

When pH< pI ?

Answer 10

amino acid will be protonated and will have an overall positive charge