VCE Chemistry Question Thread

[Billuminati]

This compound is a good example of the issues with the cis/trans nomenclature. Depending on which chemist you talk to, you will get a different answer. For the Z configuration (the original molecule) some might say it is the cis isomer because the two groups of highest priority are on the same side. However, other chemists may say that it is the trans isomer because the two longest chains are on opposite sides.

At Monash chem we kind of have to follow the Cahn Ingold Prelog rules at all times so we have to go with the highest priority, but I'm pretty sure this stuff isn't assessed in detail for high school and if it is, it would probably just be something like asking u for cis or trans but-2-ene. I heard the longest carbon chain system is the outdated system, but in any case you're right in that E/Z is the most unambiguous convention

[Chocolatepistachio]

oh ok thanks
so if you don't condense it would look like this showing the double bond

[Billuminati]

oh ok thanks
so if you don't condense it would look like this showing the double bond

You’ve shown the double bond correctly but the fluorine still needs to be on carbon 3, not carbon 2 as you’ve drawn it

[Chocolatepistachio]

So if the F is moved to carbon 3 then would it be right but then it doesn’t have bond angles of 120°  right

[Billuminati]

So if the F is moved to carbon 3 then would it be right but then it doesn’t have bond angles of 120°  right

I'm sorry if I don't understand how you worded your question, however you can still have a bond angle of 120° when F is on C3 like I've drawn in red in my other answer. Remember that this VSEPR stuff isn't assessable by VCAA. You let the COOH carbon be C1 and count from there, you'll see on my structure that the  F is on C3 and has sp2 hybridisation (120° bond angles)

[miyukiaura]

Hey guys,
I was just wondering if we needed to know the combustion products of biodiesel and petrodiesel such as nitrogen oxides, sulfur dioxides, and unburned hydrocarbons, and which ones biodiesel and petrodiesel produce more or less of compared to eachother.
Thanks

[Billuminati]

Hey guys,
I was just wondering if we needed to know the combustion products of biodiesel and petrodiesel such as nitrogen oxides, sulfur dioxides, and unburned hydrocarbons, and which ones biodiesel and petrodiesel produce more or less of compared to eachother.
Thanks

You don't need to write the impurities in an equation, but you need to be able to explain why biodiesels are more environmentally friendly than petrodiesel using the presence/absence of impurities (due to petrodiesel producing SO2 as side products, which eventually forms H2SO4 in the atmosphere which causes acid rain. Biodiesels on the other hand don't produce sulfur-containing byproducts when burnt)

[redset8]

Hi,
I'm a bit stuck with the following question.
Draw a table to predict the expected proton NMR spectrum, including expected chemical shift, relative peak area, and splitting pattern
For a start, what is this molecule called in IUPAC naming? (also I'm running off the H-NMR details from the VCAA data book)
So I'm thinking there should be 3 hydrogen environments... I think the one off the OH at the end becomes a 'singlet', but other than that I'm a bit stuck.
Any tips would be appreciated! Thanks!

[sweetcheeks]

Hi,
I'm a bit stuck with the following question.
Draw a table to predict the expected proton NMR spectrum, including expected chemical shift, relative peak area, and splitting pattern
For a start, what is this molecule called in IUPAC naming? (also I'm running off the H-NMR details from the VCAA data book)
So I'm thinking there should be 3 hydrogen environments... I think the one off the OH at the end becomes a 'singlet', but other than that I'm a bit stuck.
Any tips would be appreciated! Thanks!

I would suggest to draw out the structure of this molecule. This will help with both the naming and the assignment of proton environments.

Any ideas on the name? You are on the right track with the proton environments. Remember for splitting, you need to consider the protons on neighbouring carbons.

[redset8]

I would suggest to draw out the structure of this molecule. This will help with both the naming and the assignment of proton environments.

Any ideas on the name? You are on the right track with the proton environments. Remember for splitting, you need to consider the protons on neighbouring carbons.

Well, I had a go at drawing it out (see attached). It's an ester I think, but how would I include the hydroxyl group at the end. It's like methanediol made the ester with ethanoic acid? And that's why there is still an -OH on the end?

In terms of the splitting, the H from the -OH becomes a singlet?
The neighbouring environment from the CH3 is the Carbon from the COO, which has no hydrogens?
The answers have two singlets and a quartet.
I'm not exactly sure how hydrogen splitting works I think...   : |

[sweetcheeks]

Well, I had a go at drawing it out (see attached). It's an ester I think, but how would I include the hydroxyl group at the end. It's like methanediol made the ester with ethanoic acid? And that's why there is still an -OH on the end?

In terms of the splitting, the H from the -OH becomes a singlet?
The neighbouring environment from the CH3 is the Carbon from the COO, which has no hydrogens?
The answers have two singlets and a quartet.
I'm not exactly sure how hydrogen splitting works I think...   : |

You are on the right track. You would name that molecule the same as any other ester. The alcohol is termed hydroxymethyl.

As for the splitting, the answer key is incorrect. You can't have only one set of peaks showing splitting, because these protons need to couple to other protons which will result in splitting for both environments. Since the carbon of the ester doesn't contain any protons you would expect there to be no splitting. As a result you will end up with three singlets.

The general rule for proton NMR (for high school at least) is that the number of peaks for a given proton environment will be n+1. Where n is the number of neighbouring protons (that is, protons on carbons next door). In general, protons on oxygen and nitrogen atoms don't exhibit splitting.

Do you know what the integration of the three peaks will be?

[redset8]

You are on the right track. You would name that molecule the same as any other ester. The alcohol is termed hydroxymethyl.

As for the splitting, the answer key is incorrect. You can't have only one set of peaks showing splitting, because these protons need to couple to other protons which will result in splitting for both environments. Since the carbon of the ester doesn't contain any protons you would expect there to be no splitting. As a result you will end up with three singlets.

The general rule for proton NMR (for high school at least) is that the number of peaks for a given proton environment will be n+1. Where n is the number of neighbouring protons (that is, protons on carbons next door). In general, protons on oxygen and nitrogen atoms don't exhibit splitting.

Do you know what the integration of the three peaks will be?

So the molecule is hydroxymethyl ethanoate?

Oooohh only singlets ok. Ah that makes so much more sense!

Integration of the three peaks?? Yeah you're going to step that one out too... (I swear, my brain just deleted all this stuff)
Is that to do with the relative ratios of peak height of hydrogen; as in 3:2:1 because there is a CH3, CH2, OH, respectively?

[Billuminati]

You are on the right track. You would name that molecule the same as any other ester. The alcohol is termed hydroxymethyl.

As for the splitting, the answer key is incorrect. You can't have only one set of peaks showing splitting, because these protons need to couple to other protons which will result in splitting for both environments. Since the carbon of the ester doesn't contain any protons you would expect there to be no splitting. As a result you will end up with three singlets.

The general rule for proton NMR (for high school at least) is that the number of peaks for a given proton environment will be n+1. Where n is the number of neighbouring protons (that is, protons on carbons next door). In general, protons on oxygen and nitrogen atoms don't exhibit splitting.

Do you know what the integration of the three peaks will be?

I'm pretty sure at VCE level they're not expected to name the ester of a diol?

[Billuminati]

So the molecule is hydroxymethyl ethanoate?

Oooohh only singlets ok. Ah that makes so much more sense!

Integration of the three peaks?? Yeah you're going to step that one out too... (I swear, my brain just deleted all this stuff)
Is that to do with the relative ratios of peak height of hydrogen; as in 3:2:1 because there is a CH3, CH2, OH, respectively?

Correct, note that sometimes OH peaks aren't observed on H NMR or only as a broad signal. This is because Hs attached to electronegative atoms like O or N are termed labile and they may have been exchanged (ie taken away) by the NMR solvent

[sweetcheeks]

So the molecule is hydroxymethyl ethanoate?

Oooohh only singlets ok. Ah that makes so much more sense!

Integration of the three peaks?? Yeah you're going to step that one out too... (I swear, my brain just deleted all this stuff)
Is that to do with the relative ratios of peak height of hydrogen; as in 3:2:1 because there is a CH3, CH2, OH, respectively?

The naming is correct. You are correct for the integration as well, its the ratio of the number of protons in each environment.

I'm pretty sure at VCE level they're not expected to name the ester of a diol?

I'm not too sure.
In the study design it says 'IUPAC systematic naming of organic compounds up to C8 with no more than two functional groups for a molecule, limited to non-cyclic hydrocarbons, haloalkanes, primary amines, alcohols (primary, secondary,
tertiary), carboxylic acids and non-branched esters.'

I guess it wouldn't be any different than a hydroxylated alkene.