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Noted, Got it "Never apply any formulae blindly (at least for H2 Chem, and at least if you're an intelligent student who seeks to understand "
great http://www.mhhe.com/physsci/chemistry/carey5e/Ch27/ch27-1-4.html
http://www.chem.ucalgary.ca/courses/351/Carey5th/Ch27/ch27-1-4.html both websites same content lol
isoelectric point
- neutral side chains
pI = 1/2 (pKa1 + pKa2)
- acidic side chains
- pI = 1/2 (pKa1 + pKa3)
- basic side chains
- pI = 1/2 (pKa2 + pKa3)
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AJC 2013 p1 qn 36.
molecule 2 can exhibit aromaticity i.e. have resonance ???
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Originally posted by Flying grenade:
AJC 2013 p1 qn 36.
molecule 2 can exhibit aromaticity i.e. have resonance ???
Obviously. You would know this if you were able to draw the mechanism between the resonance contributors and hence resonance hybrid. -
ajc 2013 p1 qn 36
why molecule 3, https://en.m.wikipedia.org/wiki/Cyclooctatetraene doesn't exhibit aromaticity and is not a planar molecule, even though all the carbons are sp2 hybridised?
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Originally posted by Flying grenade:
ajc 2013 p1 qn 36
why molecule 3, https://en.m.wikipedia.org/wiki/Cyclooctatetraene doesn't exhibit aromaticity and is not a planar molecule, even though all the carbons are sp2 hybridised?
Why should a molecule be planar just because all C atoms present are sp2 hybridized? Just because benzene is so, doesn't mean all molecules are so. That's a erroneous fallacious assumption on your part.Cyclooctatetraene isn't aromatic because in addition to being non-planar, the no. of pi electrons fail to satisfy Huckel's Rule.
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https://en.m.wikipedia.org/wiki/Cyclobutadiene
this also antiaromatic ?
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Originally posted by Flying grenade:
https://en.m.wikipedia.org/wiki/Cyclobutadiene
this also antiaromatic ?
Yes, obviously. -
C10H10
Cyclodecapentaene or [10]annulene is an annulene with molecular formula C10H10. This organic compound is a conjugated 10 pi electron cyclic system and according to Huckel's rule it should display aromaticity. It is not aromatic, however, because of a combination of steric strain and angular strain.
https://en.m.wikipedia.org/wiki/Cyclodecapentaene
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Yo ultima, did u sit for the pract ??
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Annulenes are completely conjugatedmonocyclic hydrocarbons. They have the general formula CnHn (when n is an even number) or CnHn+1 (when n is an odd number).
https://en.m.wikipedia.org/wiki/Annulene
this is a great article
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good article
Comparing Aromaticity, Antiaromaticity and Non-aromaticity
https://en.m.wikipedia.org/wiki/Antiaromaticity
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https://en.m.wikipedia.org/wiki/Cyclooctadecanonaene
this guy is aromatic
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Originally posted by theophilus:
Yo ultima, did u sit for the pract ??
I can neither confirm nor deny sitting for the pract. -
Originally posted by Flying grenade:
good article
Comparing Aromaticity, Antiaromaticity and Non-aromaticity
https://en.m.wikipedia.org/wiki/Antiaromaticity
Oh yes very good article indeed, and good choice to spend the little bit of time left reading all about Uni level Chem, and still fail your H2 Chem. -
Originally posted by UltimaOnline:
Why should a molecule be planar just because all C atoms present are sp2 hybridized? Just because benzene is so, doesn't mean all molecules are so. That's a erroneous fallacious assumption on your part.Cyclooctatetraene isn't aromatic because in addition to being non-planar, the no. of pi electrons fail to satisfy Huckel's Rule.
Siala. quite difficult
cos we learn that sp2 hybridisation is trigonal planar
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Originally posted by Flying grenade:
Siala. quite difficult
cos we learn that sp2 hybridisation is trigonal planar
Just because sp2 hybridisation is trigonal planar, doesn't mean a molecule with all C atoms being sp or sp2, has to be planar. Here's a simple example to illustrate this.
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then how do we deduce if any given molecule is planar anot ?
means we can't deduce if any given molecule is planar or not, even with the ability to deduce hybridisation and given the non 3d projections(i .e. no dash wedge line shown) but given drawn chemical kekule/lewis structure ? -
unless we can somehow deduce, or have the chemical knowledge , by just looking at the non 3d structure of various molecules such as allenes and annulenes and cycloalkanes , they have to conform to some other conformations due to steric strain/angle strain/ring strain/vdw repulsions/torsional strain
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Cambridge won't ask us to draw 3D structures beyond H2 chemistry knowledge ? so we no need know
not impt, but for the love of chemistry good to know
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Originally posted by Flying grenade:
then how do we deduce if any given molecule is planar anot ?
means we can't deduce if any given molecule is planar or not, even with the ability to deduce hybridisation and given the non 3d projections(i .e. no dash wedge line shown) but given drawn chemical kekule/lewis structure ?unless we can somehow deduce, or have the chemical knowledge , by just looking at the non 3d structure of various molecules such as allenes and annulenes and cycloalkanes , they have to conform to some other conformations due to steric strain/angle strain/ring strain/vdw repulsions/torsional strain
By looking at the entire structure case-by-case and applying your knowledge of different aspects of chemistry in combination.You seem to be whining for a super simple easy way to tell if a molecule is planar or not. Such simple easy ways are for Ordinary O Level Chemistry, not Advanced A Level Chemistry.
Of course, Cambridge will use an appropriate range of difficulty in their questions. They may ask on super easy structures, or average difficulty intermediate structures, or slightly beyond A levels difficult structures (for A grade questions, only a few of such questions will appear in every paper, you shouldn't worry about such questions, it's a bell-curve, just do your best, and see if you're better than the rest).
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yep. also , even linear or trigonal planar can be on different planes
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Originally posted by Flying grenade:
yep. also , even linear or trigonal planar can be on different planes
Obviously. -
LOL wattt ?? haha its was freaking hard sia jknfsdjkfn. But just asking if priv candidates technically take a completely different paper 5 from paper 4, it cant make sense to bell curve together ehhhhh .... i know abit futile to discuss but i figured with experience you might have noted some inidcators to back my hypothesis ??? otherwise... ALL THE BEST TO ME
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Originally posted by theophilus:
LOL wattt ?? haha its was freaking hard sia jknfsdjkfn. But just asking if priv candidates technically take a completely different paper 5 from paper 4, it cant make sense to bell curve together ehhhhh .... i know abit futile to discuss but i figured with experience you might have noted some inidcators to back my hypothesis ??? otherwise... ALL THE BEST TO ME
Hard meh? Well I wouldn't know that either way (whether I took it or not). Lol.School candidates take SPA and not Pract paper, so it's meaningless to ask whether school candidates take the 'same' Pract paper or not.
For 2017 syllabus onwards though, when there's no more SPA, school candidates and private candidates will take the same Pract paper.
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LOLOL
But essentially they are 2 different papers altogether ah and im not even gonna mention the help availed. So only have 3 conclusion
1. They just hantam everything into one bell curve and ignore the difference
2. paper 5 candidates and paper 4 candidates individual bell curve
3. Or somehow they bell curve only the theory papers together and separate paper 5 and 4 for inidividual bell curves and add them back separately
For 2017 syllabus onwards though, when there's no more SPA, school candidates and private candidates will take the same Pract paper.
But this point like quite indicative that maybe point 1 can eliminate because cambridge might have identified this issue or it could be they dont feel its effecient way to learn practical skills, then begs the question why not have it as everyone take paper 5 in the first place hmmmmmmmmmmmm... once again meaningless all speculative but really quite pek cek, and this kinda constitutes a h2 chem question ?? haha sorry
