A level chemistry :Organic
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Hi everybody
I had a problem with organic chemistry - part mechanism.
There are 6 types of mechanism which I'm struggling with:
_ Free radical reaction : + Subsitution
+ Addition
_ Nucleophillic reation + Subsitution
+ Addition
_ Electrophillic reaction + Subsitution
+ Addition
How to distinguish those reaction??? I often meet a question : Which types of mechanism of following reaction ? and i don't know how to find it.
Someone help me please
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Originally posted by Theplayfulgirl brainy:
Hi everybody
I had a problem with organic chemistry - part mechanism.
There are 6 types of mechanism which I'm struggling with:
_ Free radical reaction : + Subsitution
+ Addition
_ Nucleophillic reation + Subsitution
+ Addition
_ Electrophillic reaction + Subsitution
+ Addition
How to distinguish those reaction??? I often meet a question : Which types of mechanism of following reaction ? and i don't know how to find it.
Someone help me please
Mechanisms are the heart of Organic Chemistry. Mastering mechanisms = mastering organic chemistry.And you cannot resolve this for yourself just by reading a single internet post by anyone.
You mentioned previously that you're self-studying. Which means, assuming you're in Singapore, you're doing private A levels instead of studying in a JC. Or are you simply studying ahead before JC begins?
Regardless, for you to properly address mechanisms and therefore all of organic chemistry, you need to do either (or both, if you can afford the time and money) of the following (again, it's not that I don't wish to help you online, but even for my own tuition students, it will take several entire lessons for them to properly understand (ie. not just memorize) what Organic Chem mechanisms are truly about).
Either
1) Find a good H2 Chem tutor. By this I mean a Chem tutor who will teach the underlying meaning of mechanisms, instead of (as most Singapore JCs do, due to time constraints in the classroom) just giving you mechanism notes and instructing you to memorize them.
And / Or
2) Find good Organic Chem books that teach via Mechanisms. The best books for this purpose are (links to purchase these books are given on my webpage)
http://infinity.usanethosting.com/Tuition/#Books_for_H2_Chemistry
and 
While the above books (by Joel Karty and David Klein, both professors of Organic Chemistry in American Universities) are the absolute best books on the planet to date, to helping the student to truly understand (not just memorize) Mechanisms, and thus to help the student to truly learn (not just memorize) Organic Chemistry; nonetheless because the books above are written for American Undergraduates (ie. American University students), hence in terms of practicality, and especially if you're on a tight budget, Singapore A level students might prefer a book that still teaches Organic Chemistry via Mechanisms, but still include all the necessary notes (including reagents and conditions for the H2 Chem syllabus), in other words the best of both worlds, tailored specifically to the Singapore-Cambridge A Level H2 Chemistry student. For such dual-purpose, the following book is unrivalled :
For the complete list of textbooks and guidebooks I recommend for Singapore-Cambridge A Levels H2 Chemistry, see my webpage :
http://infinity.usanethosting.com/Tuition/#Books_for_H2_Chemistry
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I'm studying with the book Advance Study Guide Chemistry. :| And the mechanism is just metioned quite slightly so i don't think it is a big problem. I understood what they wrote in the book but still cannot solve that question.. So I think i need someone to summary them in order.:)
Anyway, thanks you. I may self-reading book.
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Ah. I had some questions:
1. pH of ethers : acidic, basic or neutral
2. The addition reaction into benzen ring (=>xycloankalines): Is it nucleophllic or electrophillic
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Originally posted by Theplayfulgirl brainy:
Ah. I had some questions:
1. pH of ethers : acidic, basic or neutral
2. The addition reaction into benzen ring (=>xycloankalines): Is it nucleophllic or electrophillic
Ethers are neutral (ie. neither acidic nor basic). Their conjugate bases are not resonance stabilized (unlike carboxylic acids, phenols or enols). Oxygen atoms are a little too electronegative to be willing to donative a dative bond to be protonated readily (unlike say, N atoms of amines). But between being an acid and being a base, ethers would rather behave as a Bronsted-Lowry base. This behaviour underscores the underlying mechanisms for both generating vs cleavage of ethers :To cleave ethers using a strong hydrohalic acid :
R-O-R + H-X ---> [R-OH-R]+ + -X ---> R-X + R-O-H
and to generate ethers, with a strong acid catalyst :
R-O-H + R-O-H + H+ ---> [R-OH2]+ + R-O-H ---> [R-OH-R]+ + H2O ---> R-O-R + H2O + H+
Mechanism :
Guys like Girls, hence Nucleophiles like Electrophiles. Only Nucleophiles have the balls (ie. lone pair, or pi bond pair) to attack (ie. donate a dative bond to) Electrophiles.
Benzene is obviously the guy (although he's a weak guy coz his balls are delocalized by resonance), who attacks the girl (though to force chemical intercourse/reaction to occur, you gotta either give the guy more balls = substitute electron-donating by resonance groups onto the benzene ring, or you gotta make the girl more chio = using a Lewis acid catalyst to induce a formal positive charge on the girl), hence all such reactions that directly involve the benzene ring guy shooting out his balls (pi electrons) to any girl electrophile, is called Electrophilic Aromatic Substitution.
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Ahha.I got them now.
And about free radical reaction,they all need uv or similar reactant, don't they? So if a reaction without uv,i can assumpt they are not free radical reactions
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Originally posted by Theplayfulgirl brainy:
Ahha.I got them now.
And about free radical reaction,they all need uv or similar reactant, don't they? So if a reaction without uv,i can assumpt they are not free radical reactions
Yes, though free radical reactions can be initiated by other conditions other than UV light, such as high temperatures, or by use of certain reagents. But for the H2 Chem syllabus, yes the typical requirement is UV light.Nonetheless, for your further reading :
http://en.wikipedia.org/wiki/Radical_polymerization -
http://www.flickr.com/photos/mabuthaodang/8421927653/in/photostream
Can you help me this question??
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Originally posted by Theplayfulgirl brainy:
http://www.flickr.com/photos/mabuthaodang/8421927653/in/photostream
Can you help me this question??
Ok, before I reveal the answer to this question, pls reply the following qns first :Are you a foreign student temporarily based in Singapore? You're from Vietnam?
Are you a private candidate? Or are you studying in a JC? Or in a private school?
Where did you get this qn from? If it's a prelim paper qn, pls specify the JC name. If your private school teacher gave you this qn, pls specify the name of the private school.
Is it the Singapore 'A' Level H2 Chemistry syllabus you're taking? If not, what's the name of the chemistry exam you're preparing for?
I'm asking these qns so I can better understand your situation, which may indirectly allow me to help you better.
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Yes. I'm from Vietnam. I will have a test to NTU soon. I asked my teacher about this but he is too lazy.@@ that why i have to ask someone else. Are you the teacher in NTU ??@@
I find this website while I'm dead because of those A level stuff and your answer is quite clear.. The content and the demonstration of my book is rather different to our book so I sometimes stuck . However, your answers help me a lot
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Originally posted by Theplayfulgirl brainy:
Yes. I'm from Vietnam. I will have a test to NTU soon. I asked my teacher about this but he is too lazy.@@ that why i have to ask someone else. Are you the teacher in NTU ??@@
I find this website while I'm dead because of those A level stuff and your answer is quite clear.. The content and the demonstration of my book is rather different to our book so I sometimes stuck . However, your answers help me a lot.
So you're taking a private NTU entrance exam? So you're not taking the Singapore A Levels H2 Chemistry exam? And you've to self-study everything (the entire A level syllabus and more) within a few weeks (when's your NTU entrance exam?) on your own? (Did you previously study Chemistry in Vietnamese language, and now you've mentally converting everything to English?) Tough. My sympathies and empathies.
(Edit : No, I'm not a NTU teacher, hehe it's ok it's true that many NUS/NTU lecturers are lazy hehe. I'm an A level Chemistry private tuition teacher, specializing in Singapore-Cambridge A level H2 Chemistry. So if you take Chemistry at Uni level after you enter NTU, I won't be able to help you with your Uni level questions here on the HomeWork Forum, as all Chem questions beyond A levels should be asked at The Chemical Forums instead).
Ok, the answer to your questions are :
iv) With 1-bromopropane, methoxide will undergo SN2, while t-butoxide will undergo E2.
b) Guys are negative, Girls are positive. Guys like Girls. Chemistry is about Love.
1 - Deprotonate the ketone (the alpha protons are slightly acidic, because the enolate conjugate based is stabilized by having its negative formal charge delocalized by resonance over both the C and the O atoms) by use of a suitable strong base (eg. lithium diisopropylamide, sterically hindered and negative formal charge on the N atom).
2 - Give the enloate ion guy (who shoots out his balls or electron pair, from the less electronegative C atom, rather than the more electronegative O atom) nucleophile, a suitably attractive n-pentylhalide girl electrophile, for him to make sweet SN2 love to.
3 - Use a hydride ion nucleophile guy (eg. from LiAlH4 in dry ether) to attack and accompany the lonesome carbonyl C atom girl electrophile (who has a partial positive charge due to both induction and resonance). The resulting alkoxide ion may be protonated (ie. give the O- guy a H+ girlfriend) via hydrolysis (the H2O molecule may be thought of as a H+ girl with a OH- boyfriend; the H+ proton girl can transfer over to change boyfriends) to generate a secondary alcohol (ie. the new couple).
4 - Dehydrate the secondary alcohol (using excess concentrated sulfuric(VI) acid, at 170 deg C; alternatively use aluminium oxide at 400 deg C, or phosphoric(V) acid at 250 deg C) to obtain the alkene.
Although 2 different alkene products may be generated (since two different alpha protons may be abstracted during the elimination mechanism), the major product will be our desired alkene, because : the more stable alkene is the alkene with the greater number of alkyl groups bonded to its sp2 hybridized C atoms, ie. the more heavily substituted alkene. This is in turn due to the mechanism : the transition state (for E2) or intermediate (for E1) may be conceptualized as a carbocation, the greater the number of electron donating (by induction and hyperconjugation) alkyl groups present, the more stable the transition state or intermediate, the lower the activation energy required, the faster the rate of reaction, and hence we get more of the product, which we accordingly label as the 'major product'.
Mechanism given here by good ol Jim Clarke, whom, together with Rod Beavon, are the two world's best A Level Chemistry websites that even Cambridge uses in setting their own A level exam papers : http://www.chemguide.co.uk/mechanisms/elim/dhethanol.html5 - Oxidize the alkene using cold, dilute KMnO4 to obtain the diol. If the temperature is not kept cold, there may be sufficient activation energy to allow oxidative cleavage to occur; pH is less important than temperature, but an alkaline pH is preferred if one wishes to obtain the diol, and acidic pH if one wishes to obtain oxidative cleavage. The reason for this is due to the different activation energies for various steps of the mechanism for the 2 pathways (dihydroxylation vs oxidative cleavage) in different pH environments.
To gain a better understanding of the underlying mechanisms for the various reagents in Organic Chemistry, the following pdf e-book is highly recommended (especially if you will be taking Chemistry at Uni level in NTU, and not just preparing yourself for the A level NTU entrance exam) :
http://masterorganicchemistry.myshopify.com/
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I'm in specialiazing Chemistry Class in Vietnam so I'm not amateur in Chemistry. The biggest barrier for me is not knowledge but the demonstration in Singapore is different to Vietnam.
The test that I will take equai with Sing-Cambridge H2 A level Chemistry so your answer is the one I need.
P/s: How do you know that I come from Vietnam...
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Originally posted by Theplayfulgirl brainy:
P/s: How do you know that I come from Vietnam...
Your cute little bunny here
whispered it to me 
All the best for your NTU entrance exam, may you successfully get into NTU, chúc may mắn!
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Can you write those stuff in equation???
The huge amounts of word blow up my brain... -
Originally posted by Theplayfulgirl brainy:
Can you write those stuff in equation???
The huge amounts of word blow up my brain...I'll summarize it for you :
step 1 : Deprotonate using LDA
step 2 : Alkylate using pentyl halide
step 3 : Reduce using LiAlH4
step 4 : Dehydrate using H2SO4
step 5 : Oxidize using KMnO4
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Can you give me a source of the transformation question?
I believe that those type of question consolidate my knowledge the most
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Originally posted by Theplayfulgirl brainy:
Can you give me a source of the transformation question?
I believe that those type of question consolidate my knowledge the most
Don't have any particular source to recommend you. Because your NTU entrance exam is neither strictly the basic A level syllabus, nor is it the entire huge Uni level syllabus. So it's difficult to recommend material or websites for something that's in between. -
No need that it comes from NTU. I just want TRANSFORMATION excercise. :)
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Originally posted by Theplayfulgirl brainy:
No need that it comes from NTU. I just want TRANSFORMATION excercise. :)
Organic Chemistry Practice Problems at Michigan State University
http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/Questions/problems.htmand
Michigan State University's Virtual Textbook of Organic Chemistry
http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/intro1.htm -
Largest Cave in the World, Vietnam's Son Doong Cave :
http://singaporeseen.stomp.com.sg/stomp/sgseen/this_urban_jungle/1574236/vietnams_largest_cave_in_the_world_can_fit.htmlBeing within the cave invokes surrealistic memories of a Hollow Earth, moreso than almost any other cave, because there's actually an entire forest within the cave (due to light entering from a collapsed section of the roof).
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I 'm not sure about what you want to say and i cannot access that page too. However, I believe that the cave in the picture is not in Vietnam. I may photoshop or something similar.
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It may be out of topic but I don't want to open a new thread with only 1 question.
The radius of ion and atom decrease in order : P 3-, S2-.Ar, Cl-.
It is Ok for the decreasing of P, S and Cl but Ar. Why it is biger than Cl-
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Originally posted by Theplayfulgirl brainy:
It may be out of topic but I don't want to open a new thread with only 1 question.
The radius of ion and atom decrease in order : P 3-, S2-.Ar, Cl-.
It is Ok for the decreasing of P, S and Cl but Ar. Why it is biger than Cl-
For A level purposes, just write the following and you'll get full marks :All of the species mentioned above are isoelectronic; as proton number increases, the nuclear charge and effective nuclear charge (since for isoelectronic species the shielding effect is exactly the same), also increases; hence the ionic/atomic radius decreases as proton number increases, from P3- to S2- to Cl- to Ar.
The tricky bit here, is that noble gases (particularly the lower periods) do not chemically combine with other atoms readily. Hence, while P, S and Cl have 4 different values for atomic radii : namely atomic, covalent, ionic and van der Waals ; however for Ar, being a noble gas element, experiments can ascertain only its van der Waals radius. This results in different values quoted from different sources, which confuse students.
For A level purposes (likely including your NTU entrance exam), you need not concern yourself with these matters. Cambridge (and probably NTU) has no wish to confuse students with such a despicable low blow, (at least ostensibly) preferring to assess students on their fundamental chemistry concepts such as the simple relationship between proton number, electron configuration, effective nuclear charge and (simple) atomic radius.
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Shielding effect is the force between outmost electron and the other electron, isn't it? Actually, I don't get used to with it. I predict it because the same no of electron but different no of proton. As a result, more proton => more electrostatic force => smaller radius
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Originally posted by Theplayfulgirl brainy:
Shielding effect is the force between outmost electron and the other electron, isn't it? Actually, I don't get used to with it. I predict it because the same no of electron but different no of proton. As a result, more proton => more electrostatic force => smaller radius
Correct. So the answer is :(largest) P3- to S2- to Cl- to Ar (smallest).