H2 Chem - Organic Chemistry
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Hi UltimaOnline,
I have 2 Organic Chem Questions from RI Prelim 2013 P1 to ask:
Q19:
How do I know that C is correct? Is it because graphite is made up of huge layers of carbon atoms, thereby having stronger intermolecular forces of attraction (or is it about efficiency in packing?)
Q37
Ans: A
Remarks: Upon the boiling of sodium hydroxide, a carboxylate salt and an alkanolamine are formed. Firstly, which is the aqueous and organic layer? I would have thought that the alkanolamine would be the aqueous layer since it has smaller number of Cs as compared to the carboxylate salt. However, the answer that 1 & 2 are correct suggests otherwise. Next, why is 3 correct - why would AgBr be formed when the Br is attached to a C=C group (thereby having partial double bond character)? Is it because the resonance between Br and C=C is not perfect due to the ineffective sideways overlap between the diffused 3p orbital with the 2p orbital of the C atom?Thank you! :)
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Originally posted by gohby:
Hi UltimaOnline,
I have 2 Organic Chem Questions from RI Prelim 2013 P1 to ask:
Q19:
How do I know that C is correct? Is it because graphite is made up of huge layers of carbon atoms, thereby having stronger intermolecular forces of attraction (or is it about efficiency in packing?)
Q37
Ans: A
Remarks: Upon the boiling of sodium hydroxide, a carboxylate salt and an alkanolamine are formed. Firstly, which is the aqueous and organic layer? I would have thought that the alkanolamine would be the aqueous layer since it has smaller number of Cs as compared to the carboxylate salt. However, the answer that 1 & 2 are correct suggests otherwise. Next, why is 3 correct - why would AgBr be formed when the Br is attached to a C=C group (thereby having partial double bond character)? Is it because the resonance between Br and C=C is not perfect due to the ineffective sideways overlap between the diffused 3p orbital with the 2p orbital of the C atom?Thank you! :)
Q19. Simple covalent molecular versus giant covalent sheets.
Q37. Ion - permanent dipole interactions are thermodynamically favoured in aqueous solvents over hydrogen bonding. And no, vinyl halides are considered resistant to hydrolysis... hint : this is a despicable trick question. ;Þ -
Originally posted by UltimaOnline:
Q19. Simple covalent molecular versus giant covalent sheets.
Q37. Ion - permanent dipole interactions are thermodynamically favoured in aqueous solvents over hydrogen bonding. And no, aryl halides are considered resistant to hydrolysis... hint : this is a despicable trick question. ;ÞErm is it because when they are treating the aqueous later they are also reacting with the organic layer since it is less dense? :/
Where is the aryl halide? I was referring to the Br attached to the alkene group in the aqueous layer (C=C-Br). I would think the C-Br can be resistant to hydrolysis since it has a partial = bond character due to resonance. However I've my doubts on the strength of the resonance too as there is ineffective sideways overlap between the diffused 4p orbital of the Br with the 2p orbital of the C atom.
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Originally posted by gohby:
Erm is it because when they are treating the aqueous later they are also reacting with the organic layer since it is less dense? :/
Where is the aryl halide? I was referring to the Br attached to the alkene group in the aqueous layer (C=C-Br). I would think the C-Br can be resistant to hydrolysis since it has a partial = bond character due to resonance. However I've my doubts on the strength of the resonance too as there is ineffective sideways overlap between the diffused 4p orbital of the Br with the 2p orbital of the C atom.
Paiseh, typo, I meant vinyl halide. What you've pointed out, is the reason why halogens are (vis-Ã -vis the benzene ring) are ortho-para directing (because they donate by resonance), but yet are deactivating (because they withdraw by induction more strongly than they donate by resonance), something not only H2 students don't realize, but even many H3 students and JC teachers themselves don't appreciate.
For this RJC qn though, it's another despicable trick altogether. I repeat : the vinyl halide doesn't undergo hydrolysis due to partial double bond character for the C-X bond in the resonance hybrid. Yet, you *do* indeed get 1 mole of AgBr(s) ppt when adding AgNO3(aq) to the aqueous layer. Why? Because this is RJC. *evil grin* -
Originally posted by UltimaOnline:
Paiseh, typo, I meant vinyl halide. What you've pointed out, is the reason why halogens are (vis-à-vis the benzene ring) are ortho-para directing (because they donate by resonance), but yet are deactivating (because they withdraw by induction more strongly than they donate by resonance), something not only H2 students don't realize, but even many H3 students and JC teachers themselves don't appreciate.
For this RJC qn though, it's another despicable trick altogether. I repeat : the vinyl halide doesn't undergo hydrolysis due to partial double bond character for the C-X bond in the resonance hybrid. Yet, you *do* indeed get 1 mole of AgBr(s) ppt when adding AgNO3(aq) to the aqueous layer. Why? Because this is RJC. *evil grin*Because there was a Br- left from the first part of the reaction.
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Originally posted by gohby:
Because there was a Br- left from the first part of the reaction.
Welcome to RJC!