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Originally posted by gohby:
Hi UltimaOnline,
I've a few questions here to consult you.
Q1: IJC/09/P1/39
In which sequence are the compounds listed in order of increasing ease of hydrolysis?
Choice 3 (chlorobenzene, chloromethane, chloroethane) is not a correct choice.
Remarks: In ascertaining the ease of hydrolysis, I'll first have to see the C-X bond strength. Since it's the same in this choice, I'll have to consider either (I) Resonance within the reactant and (II) stability of the intermediate products.
In this case, shouldn't 3 also be correct? What's the difference in the electron donating effect between the methyl and ethyl substituent?
Q2: In relation to VJC/09/P1/29:
Remarks: How do I establish the relative acidity of an alcohol (CH3CH2OH) to that of an acidic salt (CH3CH2NH3+Cl-)?
Q3: VJC/09/P1/23
Remarks: It must have been my blind spot, but why is A not an acceptable answer as well?
Thank you very much Ultima!
Hi Gohby, no prob.Q1. The diff btwn Me and Et groups, is the stability (and hence Ea required) of the intermediate (if SN1) or transition state (if SN2). Et group is more strongly electron-donating by induction, which can better stabilize the intermediate or transition state.
Q2. Acidic salts (notice the adjective?) are always more acidic than alcohol (which is considered neutral, and even less acidic than neutral water).
Q3. A is the *only* acceptable answer.
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Originally posted by UltimaOnline:
If you're a BedokFunland JC student, you'll be exam-smart enough to write out both answers, with qualifications, ie. "If this solvent is used, this product is obtained ; if that solvent is used, that product is obtained". Cambridge examiner will exclaim, "Excellent student! Must be BedokFunland JC!"if solvent used in water is straightforward, tri substitution, if solvent ccl4 is used, will there be di substitution? as there is two OH groups directly attached to benzene
3 possible products if monosubstitution occurs, 5 possible products in total if di substitution and mono substitution occurs
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Originally posted by Flying grenade:
if solvent used in water is straightforward, tri substitution, if solvent ccl4 is used, will there be di substitution? as there is two OH groups directly attached to benzene
3 possible products if monosubstitution occurs, 5 possible products in total if di substitution and mono substitution occurs
Then draw all possible answers with brief explanations. -
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i thought need to have NaOH (aq) warm, to react with chloroalkane before there will be free Cl- to react with Ag+ in AgCl? is that a printing error, or how can the little amount of OH- present in AgNO3(aq) react with the chloroalkane to produce AgCl ah?
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Originally posted by Flying grenade:
i thought need to have NaOH (aq) warm, to react with chloroalkane before there will be free Cl- to react with Ag+ in AgCl? is that a printing error, or how can the little amount of OH- present in AgNO3(aq) react with the chloroalkane to produce AgCl ah?
OH- being a stronger nucleophile than H2O increases the rate of reaction (hydrolysis then ionic precipitation). But the reaction will still proceed (albeit a lot more slowly) at rtp and at neutral pH. The exothermic ionic precipitation shifts the position of equilibrium over to the RHS and makes the reaction thermodynamically feasible. But the kinetics is influenced by temperature and strength of nucleophile. -
Originally posted by UltimaOnline:
OH- being a stronger nucleophile than H2O increases the rate of reaction (hydrolysis then ionic precipitation). But the reaction will still proceed (albeit a lot more slowly) at rtp and at neutral pH. The exothermic ionic precipitation shifts the position of equilibrium over to the RHS and makes the reaction thermodynamically feasible. But the kinetics is influenced by temperature and strength of nucleophile.the OH- is from H2O
okay thanks Ultima for your reply, I've understood alr !!
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page 187
Density of water is 1000kg/m3 = 1kg/dm3 = 1g/cm3 .
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Originally posted by Flying grenade:
page 187
Density of water is 1000kg/m3 = 1kg/dm3 = 1g/cm3 .
Your many posts with no question in it is getting increasingly annoying. If there's no question, don't post. If you've a question, phrase it properly. -
Originally posted by UltimaOnline:
Your many posts with no question in it is getting increasingly annoying. If there's no question, don't post. If you've a question, phrase it properly.i am giving the correct corrections. i thought that will be good. for future readers reading cs toh's and george chong's made easy books that could have possibly come across this chem thread.
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Originally posted by Flying grenade:
i am giving the correct corrections. i thought that will be good. for future readers reading cs toh's and george chong's made easy books that could have possibly come across this chem thread.
Then say so lah. Many of your posts you just type some statements, with no clear question. Annoying coz I dunno if you need me to reply or if you need my help or not. In future, specify with something like : "This post is for information only. Coz I'm a good man who loves to help my fellow JC students." or something to that effect. -
Originally posted by UltimaOnline:
Then say so lah. Many of your posts you just type some statements, with no clear question. Annoying coz I dunno if you need me to reply or if you need my help or not. In future, specify with something like : "This post is for information only. Coz I'm a good man who loves to help my fellow JC students." or something to that effect.Thanks Ultima god! !!
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generally, increase in temperature increases solubility of ionic compounds.
page 138 organic made easy book
test for haloalkanes
heat with naoh. cool. acidify with hno3. add agno3.
my friend ask me why need cool in step 2. i dk how to answer.
is it cos temp higher so AgX cannot be precipitated? if we do all steps except/without cooling, when the solution reaches room temperature, will AgX be precipitated?
thanks ultima
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Originally posted by Flying grenade:
generally, increase in temperature increases solubility of ionic compounds.
page 138 organic made easy book
test for haloalkanes
heat with naoh. cool. acidify with hno3. add agno3.
my friend ask me why need cool in step 2. i dk how to answer.
is it cos temp higher so AgX cannot be precipitated? if we do all steps except/without cooling, when the solution reaches room temperature, will AgX be precipitated?
thanks ultima
Yes. Because higher temperature thermodynamically favors the positive entropy change of (s) --> (aq) -
Originally posted by UltimaOnline:
Yes. Because higher temperature thermodynamically favors the positive entropy change of (s) --> (aq)so can cool before and after , no issue?
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Originally posted by Flying grenade:
so can cool before and after , no issue?
What did Chan KS write? What did CS Toh write? What do u think? This sort of little KUCING KURAP why don't you have the independence to decide for yourself lah! -
thanks god. ks chan org chem book page 195 . found it
thanks !!!
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page 196 org made easy book
what is protonated alcohol? can't figure out from the mechanism at btm of page.
for the mechanism at btm of page, shld the arrow from Lone pair of alcohol reach the delta positive O ? it shld right?
many mistakes this book presented, but i learn alot from this book also. still will recommend to jc students.
i dun understand/cant decipher the mechanism in page 196.
can help check and help me improve and correct this, thank you ultima
https://www.dropbox.com/s/2ymnjkasbpi4qtn/20160822_183400.jpg?dl=0
there's also a mechanism for the formation of diethyl ether in here
https://en.m.wikipedia.org/wiki/Ether
dk how reconcile the george chong mechanism on this symmetrical ether
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Originally posted by Flying grenade:
page 196 org made easy book
what is protonated alcohol? can't figure out from the mechanism at btm of page.
for the mechanism at btm of page, shld the arrow from Lone pair of alcohol reach the delta positive O ? it shld right?
many mistakes this book presented, but i learn alot from this book also. still will recommend to jc students.
i dun understand/cant decipher the mechanism in page 196.
can help check and help me improve and correct this, thank you ultima
https://www.dropbox.com/s/2ymnjkasbpi4qtn/20160822_183400.jpg?dl=0
there's also a mechanism for the formation of diethyl ether in here
https://en.m.wikipedia.org/wiki/Ether
dk how reconcile the george chong mechanism on this symmetrical ether
"What is protonated alcohol?"-_-" If you don't even know this, how are you gonna sit for your A level exams in 2 months' time? -_-"
George Chong merely left out 1 curved arrow (the elimination of H2O+ as H2O), otherwise the rest of the mechanism is correct. But *you* totally screwed up his mechanism with your erroneous curved arrows.
If you don't understand his mechanism. then you need your school teacher or private tutor to explain the mechanism to you in-person. Move on.
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Originally posted by UltimaOnline:
"What is protonated alcohol?"-_-" If you don't even know this, how are you gonna sit for your A level exams in 2 months' time? -_-"
George Chong merely left out 1 curved arrow (the elimination of H2O+ as H2O), otherwise the rest of the mechanism is correct. But *you* totally screwed up his mechanism with your erroneous curved arrows.
If you don't understand his mechanism. then you need your school teacher or private tutor to explain the mechanism to you in-person. Move on.
got what is protonated alcohol liao.
ok noted. thanks ultima
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posting for info.
https://en.m.wikipedia.org/wiki/Methacrolein
2-Methylprop-2-enal.
interesting structure. contains aldehyde and alkene functional group.
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pg 229. George chong writes lonepair on sp3 hybridised orbital of O , again. is this erroneous?
how to tell when O and N is sp2 or sp3 hybridised?
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pg 231 top of page i think he meant chromium trioxide, CrO3, instead of dichromate
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Originally posted by Flying grenade:
pg 229. George chong writes lonepair on sp3 hybridised orbital of O , again. is this erroneous?
how to tell when O and N is sp2 or sp3 hybridised?
Sterces Edart.