Will
In uni chem you learn that you wouldn't use acidified dichromate (Jones reagent) or acidified permanganate if you want an aldehyde final product because they're strong oxidising agents that will oxidise any aldehyde formed into a carboxylic acid. You'd use Swern's reagent or Ley's reagent (TPAP) if you want to oxidise a 1Ëš alcohol to an aldehyde because they're weaker oxidants that don't over-oxidise the alcohol to a carboxylic acid
VCE Chem Questions Thread
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God
I know it's what your teacher may have taught you (I was taught that mild oxidation under 60ËšC produces aldehydes in high school too), but this one of those really shameless lies taught in VCE chem. Acidified permanganate or dichromate is aqueous, and in aqueous solutions, aldehydes react with H2O to form geminal diols (an alcohol that has 2 hydroxyl groups attached to the same carbon). Hence you can't actually make a pure sample of aldehyde with the oxidising reagents you learned about in VCE, only its geminal diol (hydrate) form which has very different chemical properties from aldehydes
I have trouble understanding hydrogen/carbon groups environments.
I can identifying them, I just seem to get tripped up on whether different hydrogens are part of the same group.
My common mistake is believing that two carbon environments are part of the same environment, when they are in reality different.
For carbon/hydrogen sections to be a part of the same environment does the molecule HAVE to be symmetrical?
If there is a H-environment identical to another in the molecule, then yes it's symmetrical. One hack I learned in uni for identifying whether or not 2 given environments are chemically equivalent is to pretend to cut off the C atom the H-environment is attached to from the rest of the molecule. You repeat it for the other environment (with a separate structure) and then you compare if the rest of the molecule is identical in both cases. If it is, then these 2 environments are equivalent (will post a visual example)
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There done, the squiggly line is just the convention we use in uni organic chem to represent a removed or arbitrary fragment.
3-pentanone example
Hi Billzene!
Quick question:
For the substitution reaction: Haloalkane + H2O(g) → Alcohol: NaOH / OH-
Is water a gas? Or a liquid?
Cheers!
Btw: Absolutely love that method for h-environments! Maybe you should be called god, lol....
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God
H2O isn't involved in the reaction converting haloalkanes to alcohols cuz it's uncharged and therefore a weak nucleophile. Unless you have a suitable catalyst, this reaction won't happen at a significant rate, that's why VCAA expects NaOH or KOH or OH-. You need OH- since converting a primary haloalkane into a primary alcohol is what we call an SN2 reaction, which requires a strong (charged) nucleophile. You may think OH- is the catalyst cuz it deprotonates water, but this isn't actually the case. You use up 1 particle of OH- to deprotonate 1 molecule H2O (making 1 particle of OH-) which then reacts with a haloalkane molecule (so you end up using 2 particles of OH- while only producing 1, for a net use of 1 OH- particle). Since catalysts by definition aren't consumed, OH- in this case is a reactant, not a catalyst
Billzene So do you think we need to include states for the reactant and catalyst in hydration of alkenes. The 2020 report just says H20 / H+, but I usually see H2O(g) and H3PO4(aq). If the alkene and water are both gases, what is the acid aqueous in? Can things dissolve in steam? Thanks heaps Bilzene!
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Also, in H-NMR, if the adjacent H on adjacent carbon atoms are in the same chemical environment (say a cycloalkane for example), is there any splitting pattern. If not, what about when the chemical environment is only slightly different, like for 2 adjacent CH2 groups in an octane molecule. Would it then be a splitting pattern with a tiny chemical shift either side?
And more importantly, does VCAA care? Thanks again.
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Jesus
That's precisely the reason VCAA doesn't ask you the states of the H3PO4 catalyst since people can debate forever about whether it's (g) or (aq). You should always write H2O (g) though
Jesus
Hs in the same environment don't split each other, so for cyclohexane, you'll just see a singlet that integrates to 12
Slightly different chemical environments do produce splits. The width of the split doesn't matter since you only deal with 3J coupling in VCE chem
Does VCAA care if we do not specify something implied during naming of a compound?
Eg. Propanone is obviously propan-2-one
Will I'm sure Billzene will be able to give you a better answer since I'm a bit out of touch with VCE chemistry, but I am pretty sure that the numbers are not necessary for compounds that are implied. For example, no need to write propan-2-one, propanone will suffice (but you actually don't need to know how to name aldehydes and ketones for VCE chemistry anyway)
Jesus
You wouldn't lose marks for writing this.
Will
It's super inconsistent. I got a mark taken off on a SAC for writing propan-2-one due to the redundant number, but when I omitted it on my exam, I got a mark taken off there. This might be bad luck since the students I tutor never lost a mark on their exams for including or excluding a redundant position number.
Hey Billzene,
Do you know if we need to know which amino acids are essential?