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发表于 22-7-2006 10:05 PM
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回复 #37 独帆 的帖子
Cl is an electron-withdrawing group, so it increase the acidity of CH2COOH.CH3 is an electron-donating group, so it stronger the O-H bond in COOH,hence it becomes less acidicty compare to CH2COOH.In the carboxylate ion(R-COO-), the negative charge is delocalised over both the electronegativity oxygen atoms, so CH3COOH more acidity than phenol.Phenol is more acidity than alcohol because benzene ring is an electron-withdrawing group.
electron-withdrawing group: increase acidicty
Eg: benzene ring, NO2
electron-donating group:decrease acidicty
Eg: CH3, OH
我这样解释对吗? |
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发表于 22-7-2006 10:08 PM
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发表于 23-7-2006 01:02 AM
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发表于 24-7-2006 03:35 PM
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发表于 26-7-2006 03:29 PM
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发表于 28-7-2006 11:40 PM
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原帖由 dunwan2tellu 于 3-7-2006 06:51 PM 发表
问题 22
When a compound X is refluxed with propanol , two compound Y,Z with molecular formula (C_6)(H_12)(O_2) and (C_5)(H_10)(O_2) respectively is ...
有compound是可以 refluxed with propanol的啊? Y&Z 是carboxylic acid吗?问题有一点怪........ |
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楼主 |
发表于 29-7-2006 11:08 AM
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原帖由 happytomato 于 28-7-2006 11:40 PM 发表
有compound是可以 refluxed with propanol的啊? Y&Z 是carboxylic acid吗?问题有一点怪........
Y & Z 其中一个是 carboxylic acid .不要忘了 ester 也是 carboxylic acid 的 isomer .
提示：esterification of anhydride |
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发表于 5-8-2006 07:40 PM
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原帖由 dunwan2tellu 于 29-7-2006 11:08 AM 发表
Y & Z 其中一个是 carboxylic acid .不要忘了 ester 也是 carboxylic acid 的 isomer .
提示：esterification of anhydride
为什么你的esterification没用conc H2SO4?还有为什么没有产生H2O?就是因为它是esterification of anhydride? |
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楼主 |
发表于 5-8-2006 08:13 PM
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原帖由 happytomato 于 5-8-2006 07:40 PM 发表
为什么你的esterification没用conc H2SO4?还有为什么没有产生H2O?就是因为它是esterification of anhydride?
普通的esterification 也就是 carboxylic acid + alcohol ( with conc H2SO4)会产生 ester + H20 .
但是 esterification of anhydride (using alcohol),会得到 ester + carboxylic acid .相关的内用应该可以从“ carboxylic acid”的 topic 得到更多资料。 |
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发表于 12-8-2006 09:37 AM
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[quote]原帖由 dunwan2tellu 于 5-8-2006 08:13 PM 发表
普通的esterification 也就是 carboxylic acid + alcohol ( with conc H2SO4)会产生 ester + H20 .
但是 esterification of anhydride (using alcohol),会得到 ester + carboxylic acid .相关的内用应该可以 ... [/quo
te]
可是esterification of anhydride不是已经不在 STPM 的syallabus里面了吗?现在的STPM书里面根本就没有anhydride的东西.答案是不是:
O
||
CH3-CH2-C
\
0 + CH3CH2CH2OH
/
CH3-C
||
O |
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楼主 |
发表于 12-8-2006 01:06 PM
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总共有 11 个 Carbon ( Y 6 个，Z 5 个），但这是加上 propanol (3 个 C) 后的，所以你的 X (也就是 anhydride)应该要有 11-3= 8 个 C .方法不只一个，其中一幅答案是
(CH3)5C00C0CH3
好吧！是时后进入 23 题
问题 23
How can we convert propan-2-ol into methyl-propanoic acid ?
[ 本帖最后由 dunwan2tellu 于 12-8-2006 01:11 PM 编辑 ] |
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发表于 12-8-2006 08:00 PM
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原帖由 dunwan2tellu 于 12-8-2006 01:06 PM 发表
总共有 11 个 Carbon ( Y 6 个，Z 5 个），但这是加上 propanol (3 个 C) 后的，所以你的 X (也就是 anhydride)应该要有 11-3= 8 个 C .方法不只一个，其中一幅答案是
(CH3)5C00C0CH3 好吧！是时后进入 23 ...
我的答案错了啊......,不知道今年的STPM会不会出像这样难的问题.请问一下,那个答案怎样画它的formula structure?谢谢...... |
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楼主 |
发表于 12-8-2006 10:08 PM
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原帖由 happytomato 于 12-8-2006 08:00 PM 发表
我的答案错了啊......,不知道今年的STPM会不会出像这样难的问题.请问一下,那个答案怎样画它的formula structure?谢谢......
差不多就是你之前画的，只是差上面部分画 6 个 C (chain 拉长一点罢了！） |
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发表于 13-8-2006 04:13 PM
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发表于 14-8-2006 11:27 PM
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Apa maksud Jelaskan secara kualitatif?
Contoh soalan:
Jelaskan secara kualitatif bagaimana tekanan wap metilbenzena berubah apabila benzena dilarut di dalamnya.
Jawapannya ialah tekanan wap metilbenzena menurun kerana pecahan mol metilbenzena berkurang. |
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发表于 14-8-2006 11:47 PM
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mengapa cecair yang bertekanan wap tinggi lebih meruap? |
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发表于 23-8-2006 11:55 PM
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问题24
Which one of thr following statement explain why the emission spectrum of atomic hydrogen consisting of discrete lines?
A.an electron can possess any amount energy
B.the electron in hydrogen atom can only occupy fixed energy levels.
C.Transition of an electron from a higher energy level to a lowerenergy level emits light
D.An emission spectrum consists of discrete lines which have fixed frequencies.
[ 本帖最后由 jayck 于 24-8-2006 08:51 PM 编辑 ] |
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楼主 |
发表于 24-8-2006 12:28 AM
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原帖由 jayck 于 23-8-2006 11:55 PM 发表
问题24
Which one of thr following statement explain why the emission spectrum of atomic hydrogen is a line spectrum?
A.an electron can possess any amount energy
B.the electron in hydrogen atom ...
Q23 还没答，Q24就出来了
答案是 C ，不知道对不对？ |
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发表于 24-8-2006 10:48 AM
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原帖由 dunwan2tellu 于 24-8-2006 12:28 AM 发表
Q23 还没答，Q24就出来了
答案是 C ，不知道对不对？
答案是B
When electron falls from a higher level to a lower level ,excess energy is given out as radiation with certain frequency.
And this frequency is determine by the two level involve in the transition,因为这只有certain discrete amount of energy可以释放出. |
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发表于 24-8-2006 11:05 AM
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问题25In the line emission spectrum of hydrogen , how many lines can be accounted for by all the possible electron transition between the five levels of lowest energy within the atom.
A. 4 B. 5 C.8 D.10 |
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