STPM化学专区

junchung2003

回复 739# 邪魅


   
- C7H8 is a benzene since C to H ratio is almost 1:1
- Does not have double bond at the chain since aqueous Br does not decolourise
- It is a methylbenzene since it does not decolourise aq Br but decolourise KMnO4
- Methylbenzene can undergo oxidation and form benzoic acid, hence, KMnO4 will be decolourise

然后你画 Methylbenzene的图。
再画Methylbenze 变去 Benzoic acid 的图，箭头上面有KMnO4这个agent

至于第二题，看下面。

-有两个可能性，
-第一个是Chloromethylbenzene
-第二个是Chlorine和Methyl group分别念在不同的benzene position
-如果最后加silver nitrate会变白色，那么就可以确定Cl是粘在Chain上面，所以上面的第二个可能性消灭。
-解释了上面，你就能画equation
-Chloromethylbenzene (C6H5CH2Cl) + NaOH --> Benzyl Alcohol (C6H5CH2OH)
-Benzyl Alcohol acidified 了变回 Chloromethylbenzene
-Hence, Silver nitrate test give white precipitates, equation 有 AgCl (White)

第二题不确定，忘记的七七八八了，希望帮到你

silent91

KMnO4 是 oxidising agent.
1.oxidising agent 会对Organic compound怎样呢？
2.KMnO4 只会 decolourise ...
邪魅 发表于 14-1-2011 10:25 PM

2) KMnO4 also decolourise primary & secondary alcohol...

红姐

谢谢各位！无限感激！

vick5821

Hey, can anyone helpout with this?

Write the equation for the preparation of propenne from 2-chloropropane..How?? By cracking??

and also outline the synthetic pathway for the formation of chlorocyclohexane from cyclohexanol

thanks

p/s : any good web recommended to study organic chem?? thanks

junchung2003

回复 747# vick5821


    2-chloropropane to propene

Process: Elimination
Reagent: Alcoholic sodium hydroxide
Condition: Reflux

cyclohexanol to chlorocyclohexane

Process: Dehydration
Reagent: Concentrated hydrochloric acid
Condition: 180 degree celcius
Product: cyclohexene

Process: Addition
Reagent: HCl
Condition: room temperature (If not mistaken)
Product: chlorocyclohexane

华语

vick5821

Elimination same as dehydration?

junchung2003

回复 749# vick5821


    elimination = eliminate hydrogen halogen
dehydration = eliminate water
话语

vick5821

but dehydration can be consider as elimination reaction rite??

junchung2003

回复 751# vick5821


    这个是concept的问题吧，因为process名字和reagent有关联，所以分清楚比较好  

莲花

non ideal solution 是不是只考graph and calculation only?

junchung2003

回复 753# 莲花


    什么款式的问题都有可能发生

vick5821

I wan to ask a ques

Outline the synthesis pathway for the formation of 1,2-dibromocyclopentane from bromocyclopentane

Using what reaction? Can I use free radical substitution of Br?

Another question

Uploaded with ImageShack.us


The reaction will occur at where wor?

thanks ^^

silent91

回复 755# vick5821

alkane only got 1 reaction (i mean for stpm syllabus)...
so i think it's correct to use free radical substitution...



*if got mistake, anyone may correct me...

破晓时分

question for chapter one..MATTER..
1. Titanium, Ti(nucleon3 and proton 1) a radioactive isotope of hydrogen, slowly turns into a helium isotope, He(nucleon3 and proton 2). which statement is true of the two isotope?
A. Ti and He have the same nuclear charge
B. Ti and He have the same number of neutral subatomic particles.
C. Ti and He have the same number of charged subatomic particles.
D. Ti and He are deflected to the same point in a magnetic field whose strength is not varied.

answer is D...谁知可以帮忙解释下。。thanks.!!

silent91

question for chapter one..MATTER..
1. Titanium, Ti(nucleon3 and proton 1) a radioactive isotope of  ...
破晓时分 发表于 11-3-2011 02:52 PM

A is wrong diff proton num therefore diff in nuclear charge.
B is wrong coz of diff in neutron num
c is wrong becoz diff in proton num
D is correct becoz there are not in ion state, therefore they will not deflect into anywhere in magnetic field.

破晓时分

A is wrong diff proton num therefore diff in nuclear charge.
B is wrong coz of diff in neutron  ...
silent91 发表于 14-3-2011 02:06 PM

   哦。。解释得很清楚。。谢谢你！！

silent91

哦。。解释得很清楚。。谢谢你！！
破晓时分 发表于 15-3-2011 09:52 AM

    sorry ya...the explanation of ans D got mistake...there is no related to ions...(long time no study dy)

what i get from internet is both atom has the similar mass, so they deflect in the same position.
this is due to the similar mass of proton & neutron...

破晓时分

sorry ya...the explanation of ans D got mistake...there is no related to ions...(long time ...
silent91 发表于 15-3-2011 03:16 PM

   ok..thanks so much..i ll post other questions here next time since tis is the only place for answering my questions..haha

silent91

ok..thanks so much..i ll post other questions here next time since tis is the only place fo ...
破晓时分 发表于 16-3-2011 08:41 AM

    因为以前，我也是靠这里的senior指点的。所以我尽力咯

破晓时分

因为以前，我也是靠这里的senior指点的。所以我尽力咯
silent91 发表于 17-3-2011 08:42 PM

   毕业了？stpm考得怎样？