Homework questions thread

[Shenz0r]

Draw out D, you'll actually see that it's a secondary alkanol (2-methylpropan-2-ol). You can't oxidise secondary alkanols into carboxylic acids, you'll form ketones instead.

A is the only primary alkanol in the options, so I would go for A.

[charmanderp]

D is actually a tertiary alcohol, so it couldn't be oxidised at all.

[destain]

what is A, is it an alcohol even
CHO

[Shenz0r]

What's the difference between a tertiary and a secondary alkanol?

[charmanderp]

The hydroxyl carbon in secondary alcohols is attached to two alkyl groups and to three alkyl groups in tertiary alcohols.

[charmanderp]

what is A, is it an alcohol even
CHO

It reads more like an aldehyde, which can indeed be further oxidised to a carboxylic acid. Are you sure it says CHO and not COH?

[jasoN-]

R-CHO is an aldehyde
It can be oxidised to a carboxylic acid, so that answer is still correct (another option would be primary alcohols R-OH)
if the alcohol is not on a terminal carbon, it can only be oxidised to a ketone (R-CO-R')

[destain]

propanal isnt an alcohol is it? so how does it go to a carboxlyic acid

[charmanderp]

Aldehydes are primary alcohols that have been partially oxidised. If you further oxidise them they will be converted to a carboxylic acid, so A is correct.

AFAIK this isn't in the VCAA Chemistry course.

[Bhootnike]

for those who have thushans book - pg 242, q1c,
Why is it that the m/z value of the largest molecular ion will increase throughout a analysis, given that we have a mixture of alkanes which are analysed through a coupling technique, where the sample is inserted into a gas chromatograph, and then travels into a mass spectrometer.

is it right that when in GC, the mixture has all the alkanes together, which are soluble in one another, but then separated due to adsorption onto s'phase. So when the largest alkane does reach the mass spec, itll be by itself?

i dont get how 'm/z of molecular ion will increase over time' 

[destain]

Hex-1,5-diene and hydrogen bromide, how many isomers..
how does it become dibromo, im not sure if this is a stupid question but i cant figure it out atm...
HBr? so shouldnt a H and a Br attach to it

[Tonychet2]

Hex-1,5-diene and hydrogen bromide, how many isomers..
how does it become dibromo, im not sure if this is a stupid question but i cant figure it out atm...
HBr? so shouldnt a H and a Br attach to it

add 2HBr so both carbon double bond is split and a H and Br attach to each

[destain]

ah okay 2HBr....
ad what does reacting under reflux mean?
does that mean it's a 1:1 ratio?

[Bhootnike]

for those who have thushans book - pg 242, q1c,
Why is it that the m/z value of the largest molecular ion will increase throughout a analysis, given that we have a mixture of alkanes which are analysed through a coupling technique, where the sample is inserted into a gas chromatograph, and then travels into a mass spectrometer.

is it right that when in GC, the mixture has all the alkanes together, which are soluble in one another, but then separated due to adsorption onto s'phase. So when the largest alkane does reach the mass spec, itll be by itself?

i dont get how 'm/z of molecular ion will increase over time'

^ this and,
is there any reason why we dont account for the double bond in carboxyl group when considering saturation of a fatty acid, and how the DBE formula does not =1 when you have a carboxyl group in a fattyacid?

[pi]

Saturation/unsaturation relates to the bonding between the carbons only, hence the C=O does not count