Experiment 8: Physical And Chem Properties Of Organic Compounds

Question 1

Explain the trend in the following melting points:
Pentane has a Mp of -129^oC,
Diet gym ether has a mp of -116^oC
1-butanol has a melting point of -90^oC

Answer 1

PENTANE:
- most C atoms = greatest surface area for van der waal’s forces to form on and act upon
= lowest melting pt => easiest to overcome

DIETHYL ETHER:
- dipole-dipole forces due to polarized C-O bond and van der waal’s forces acting on it = more energy required to overcome intermolecular forces

1-BUTANOL:
- hydroxyl group => hydrogen bonds
=> requires most energy to overcome

Question 2

What would you expect the product of the reaction of cyclohexane with Br_2 to be?
What type of rxn is it?
Is it the same type of reaction as occurred between phenol and Br_2 in exercise 9.

Answer 2

C_6H_12 + Br_2 —> C_6H_12Br_2

• 1,2-dibromhexane would be the product
• it is an addition rxn, namely a halogenation rxn
• no, it is not the same because the reaction that occurs between phenol and Br_2 is a substitution rxn where decolourization occurs and hydrogen bromide would form as a product

Question 3

What can you deduce about the structure of unknown A

Answer 3

It turned orange/. Row. With Br_2 so it is saturated and it remained purple
= it is structurally similar to cyclohexane

Question 4

Would you expect the mo of 1,4- dimethyl benzene (p-xylene) to be higher or lower than that of p-toluic acid?
Explain your answer

Answer 4

The mp of 1,4- dimethylbenzene would be expected to be lower than that of p-Toulic acid (being an acid) contains a COOH group
= more energy required to overcome hydrogen bonds in p-toluic acid than the London forces in 1,4 dimethylbenzene —> p-Toluic acid has a higher melting point