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Originally posted by Flying grenade:
eh
i worked out d.o.u. of benzene =4 .
D.O.U.(benzene) = (14-6)/2 =4
Look at the *structure* (not the Singapore JC guniang-sissy version with the circle in the middle, ie. resonance hybrid ; but use the Uni level garang-gungho version with alternating double and single bonds, ie. resonance contributor) of benzene, and explain exactly why the d.o.u. for each benzene ring is 4. -
Originally posted by UltimaOnline:
Look at the *structure* (not the Singapore JC guniang-sissy version with the circle in the middle, ie. resonance hybrid ; but use the Uni level garang-gungho version with alternating double and single bonds, ie. resonance contributor) of benzene, and explain exactly why the d.o.u. for each benzene ring is 4.to explain why d.o.u. of benzene is 4, isn't the evidence/reason my calculation workings?
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hmm, if use words and explain, is it becos the index of hydrogen deficiency of benzene is four??
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anyway im more stress abt this qn now : for the A level 2015 p3 qn 1 question, we calculated dou is 3. but the molecule only gt 2 double bonds. one double bond = 1 dou
what shld i do?? what shld i learn from 3 dou? teach me ultima T-T
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Originally posted by Flying grenade:
anyway im more stress abt this qn now : for the A level 2015 p3 qn 1 question, we calculated dou is 3. but the molecule only gt 2 double bonds. one double bond = 1 dou
what shld i do?? what shld i learn from 3 dou? teach me ultima T-T
Figure this out yourself. What's the definition of D.O.U.???Super Coconaden Hint for Super Coconaden pple : obviously it can't be just double bonds which affect degree of unsaturation!!! *Sheeeesh
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eh so what is your correct explanation of why dou of b.ring is 4?? have other explanations other than the mathematical calculation?
share other explanations too please !
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ok yes, right. not only double bonds affect dou
a cyclic ring formed by 6 C atoms is one dou unit is it?
then what's the beauty/usefulness of dou?
to check >4 or <4 only?
or is it like for me to narrow down guesses, maybe like, the molecule could probably have two double bonds, and one ring made up of 6 C atoms?
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Originally posted by Flying grenade:
ok yes, right. not only double bonds affect dou
a cyclic ring formed by 6 C atoms is one dou unit is it?
then what's the beauty/usefulness of dou?
to check >4 or <4 only?
or is it like for me to narrow down guesses, maybe like, the molecule could probably have two double bonds, and one ring made up of 6 C atoms?
So what's the *definition* of D.O.U? Why must the ring consist of 6 C atoms? -
exactly la sia. ring need not be formed by 6 C atoms only. THEN HOW SIAAA. ring how?? T_T how to handle rings , when we dk how many C atoms in rings??
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is the definition of dou index of hydrogen deficiency? how many H atoms the molecule is deficient , from the theoretical saturated form?
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can't find definition of d.o.u. online :'(
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is it becos ring made up of 6 C atoms, then its like equivalent to three double bonds(also made up of three atoms). no wait wrong.
becos ring of 6C is C6H12 and hence 1DOU cos just need two more H atoms to be fully saturated? ?
this very good article also keep using the term 'ring' , i think it's referring to ring made up of 6 C, the article didn't qualify why 6C
http://chem.libretexts.org/Core/Organic_Chemistry/Hydrocarbons/Alkenes/Properties_of_Alkenes/Degree_of_Unsaturation
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Originally posted by Flying grenade:
can't find definition of d.o.u. online :'(
Wow, Wikipedia must have moved to the dark deep web, no wonder you can't find it. -
Originally posted by Flying grenade:
can't find definition of d.o.u. online :'(
Even if Wikipedia or other sites don't directly spoonfeed you the definition, Cambridge can (in a challenging A grade H2 Chem A level exam question) give you formula for degree of unsaturation, and ask you to concordantly suggest a definition for the term. -
saw wiki page on dou liao.
no have defn for it. also nvr say why ring is 6 C atoms.
just now , was the explanation u were looking for this?
Benzene rings count as four degrees of unsaturation, since they consist of one ring and three pi bonds.
(math calculation of 4 also gd, i calculated that before thinking abt b contains 1 ring and 3 pi bonds)then is it based on this, so ring is made up of 6C ah -
i got it alr
For instance, a degree of unsaturation of 3 can contain 3 rings, 2rings+1 double bond, 1 ring+2 double bonds, 1 ring+1 triple bond, 1 double bond+1 triple bond, or 3 double bonds.
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Originally posted by Flying grenade:
saw wiki page on dou liao.
no have defn for it. also nvr say why ring is 6 C atoms.
just now , was the explanation u were looking for this?
Benzene rings count as four degrees of unsaturation, since they consist of one ring and three pi bonds.
(math calculation of 4 also gd, i calculated that before thinking abt b contains 1 ring and 3 pi bonds)then is it based on this, so ring is made up of 6C ah
Obviously, benzene ring of course consists of 6 C atoms, but are you saying if a ring has less or more than 6 C atoms, it has 0 d.o.u.?!!?!?!!?!???If so, I give up on you. Go ask your school teacher or private tutor.
If not, then why do you keep OCDing about "6 C atoms" when we're talking about the meaning of d.o.u (and not just benzene rings)?!?!?!?!!?
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lagged post sorry ,due to technical faults, i intended to post this earlier
ok ultima i got it alr.
i clarified my doubts on dou liao. i know how do the 2015 qn liao
dont press u on this topic liao, i settled and clarified liao
Thanks Ultima so much for guiding and replies
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Originally posted by UltimaOnline:
Obviously, benzene ring of course consists of 6 C atoms, but are you saying if a ring has less or more than 6 C atoms, it has 0 d.o.u.?!!?!?!!?!???If so, I give up on you. Go ask your school teacher or private tutor.
If not, then why do you keep OCDing about "6 C atoms" when we're talking about the meaning of d.o.u (and not just benzene rings)?!?!?!?!!?
no thats not what i meant lar!! i was wondering of ring more or less than 6 C atoms, then how ?
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Originally posted by Flying grenade:
no thats not what i meant lar!! i was wondering of ring more or less than 6 C atoms, then how ?
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i know liao. then just use other chemistry knowledge, logic, analysis, reasoning, clues and information given in qn, to solve the qn.
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Originally posted by UltimaOnline:
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.
Hello UltimaOnline,
Regarding Q3 (VJC/09/P1/23), What's wrong with choice B in fulfilling all the conditions? It reacts with bromine because of the C=C bond, it has 2 Cl substituents which will become 2 alcohol groups in the presence of hot alkaline and it reacts with PCl5 because of the carboxylic acid.
2014/HCI/P1/Q40
Which site gets deprotonated first? I'd have thought that in a neutralisation reaction with a base the most acidic component will be deprotonated first (i.e. the NH3+), followed by the COOH not connected to the CH2, followed by the last COOH. Is my understanding correct? (the answer scheme suggests otherwise)
Thank you :)
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Originally posted by gohby:
Hello UltimaOnline,
Regarding Q3 (VJC/09/P1/23), What's wrong with choice B in fulfilling all the conditions? It reacts with bromine because of the C=C bond, it has 2 Cl substituents which will become 2 alcohol groups in the presence of hot alkaline and it reacts with PCl5 because of the carboxylic acid.
2014/HCI/P1/Q40
Which site gets deprotonated first? I'd have thought that in a neutralisation reaction with a base the most acidic component will be deprotonated first (i.e. the NH3+), followed by the COOH not connected to the CH2, followed by the last COOH. Is my understanding correct? (the answer scheme suggests otherwise)
Thank you :)
Hi Gohby,VJC qn : geminol diols spontaneously dehydrate into into carbonyl compounds with thermodynamically favourable positive entropy change. H3 syllabus stuff, but has been asked many times in H2 Prelim papers.
HCJC qn : yes you're right that the most acidic proton is abstracted away first. Most acidic to least : alpha COOH, R group COOH, alpha NH3+, R group NH3+.
No prob :)