Dark Horse's Questions

[Dark Horse]

Hey guys, doing StudyOn trial exam, need to clarify a few questions:

M.C Question 1
In TLC, the stationary phase used is made of Aluminium Oxide. Which of the following molecules would be expected to have the smallest Rf using TLC?
a) hexanoic acid
b) pentan-1-ol
c) 1 amino butane
d) pentane
What would the answer be? Could someone pls explain it?

M.C Question 3
Which of the following molecules could be distinguished from the other molecules due to the absence of a particularly distinct and characteristic peak using IR Spectroscopy?
a) butan-1-ol
b) butanoic acid
c) 1 amino butane
d) methyl butanoate

Also, a short answer question is all about how the esters in perfume are analysed using HPLC. The question asks why HPLC was used in preference to GC? The answers say biological molecules are heat sensitive. What does this mean, and is it right?

Finally, what is a hydrolysis substitution reaction? Do we need to know about it in VCE?

Thanks in advance

[chem-nerd]

M.C Question 1
In TLC, the stationary phase used is made of Aluminium Oxide. Which of the following molecules would be expected to have the smallest Rf using TLC?
a) hexanoic acid
b) pentan-1-ol
c) 1 amino butane
d) pentane
What would the answer be? Could someone pls explain it?
you'd want to select the largest (harder to move through the stationary phase), most polar (most attracted to the stationary phase) molecule, hence A

M.C Question 3
Which of the following molecules could be distinguished from the other molecules due to the absence of a particularly distinct and characteristic peak using IR Spectroscopy?
a) butan-1-ol OH peak at 3570-3200
b) butanoic acid OH peak at 3500-2500
c) 1 amino butane NH peak at 3500-3300
d) methyl butanoate will not have a peak in this region. the CH peak at 2960-2850 will be strong as compared to the OH peak in butanoic acid which will be broad

Also, a short answer question is all about how the esters in perfume are analysed using HPLC. The question asks why HPLC was used in preference to GC? The answers say biological molecules are heat sensitive. What does this mean, and is it right?
It's true that biological molecules are heat sensitive and therefore not usually analysed using GC. This is one of those ambiguous questions as you would usually analyse perfumes using GC due to them being volatile.

Finally, what is a hydrolysis substitution reaction? Do we need to know about it in VCE?
Yes you do need to know about these. Hydrolysis reactions are those in which water is a reactant. An example of a hydrolysis substitution reaction would be converting a chloroalkane into an alkanol.