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https://www2.chemistry.msu.edu/faculty/reusch/virttxtjml/sterisom.htm
Note that cycloalkenes smaller than eight carbons cannot exist in a stable trans configuration due to ring strain.
pls take a look at my qn on pg 47 of this thread, btm of page
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Lmao
http://chemistry.stackexchange.com/questions/30940/cis-trans-stability-of-cycloalkenes
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a response from the above post : "...trans-cyclododecene (12 carbons) do you have enough carbons to easily connect from one end of the trans double bond back to the other end. Trans-cycloalkenes with less than 12 carbons have additional strain because of this difficulty in spanning the double bond. "
ps, difficult to edit the post above, with a picture attached, using handphone, hence this related but detached post
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not very useful
https://en.m.wikipedia.org/wiki/Ring_strain
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Hi UltimaOnline, just a little concept clarification. Is there a buffer region for weak acid and weak base titration? Thanks
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Originally posted by MightyBiscuits:
Hi UltimaOnline, just a little concept clarification. Is there a buffer region for weak acid and weak base titration? Thanks
Technically, yes. Buffer regions still occur when you've close to equal molarities of HA and A-, as well as close to equal molarities of B and BH+ (note that the actual maximum buffer capacities of the solution, however, is no longer based simplistically on having equal molarities of both members of each conjugate acid-base pair, since the other conjugate acid-base pair also exerts its influence on pH and buffering capacity; exact calculations here are significantly beyond the scope of A levels).In addition, there is an additional (albeit weaker) buffer region (unique to weak acid - weak base titrations) that spans from the 1st buffer region (ie. near half-equivalence point) all the way to the 2nd buffer region (ie. near double-equivalence point), including the titration equivalence point, since both cation and anion of the salt at equivalence point, are themselves a weak acid and a weak base.
If Cambridge were to ask Singapore students to calculate the pH at equivalence point of a weak acid - weak base titration, 99.99% of Singapore H2 Chem students (and even many JC teachers and private tutors) would die. But if you're interested to challenge yourself, try solving such a question. Hint : you'll need to solve simultaneous equations which takes into account the simultaneous hydrolysis of both cation and anion of the salt.
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pg 23 george chong org chem book
btm of page
what does he mean by two hydrogens?
there are 3 different types of hydrogen in that ethanol molecule.
nt sure but i dont think he meant by the mass number of deuterium?
i thought enantiomers have similar physical and chemical properties (unlike diastereomers) , except their effect on plane polarised light(PPL) only?
the two enantiomers exhibit different chemical shifts in NMR?
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https://en.m.wikipedia.org/wiki/Nuclear_magnetic_resonance_spectroscopy_of_stereoisomers
ok i will move on. know the primary qn can liao, the molecule is chiral. hope u can elaborate on my above query if can
Thanks Ultima !
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Originally posted by Flying grenade:
https://en.m.wikipedia.org/wiki/Nuclear_magnetic_resonance_spectroscopy_of_stereoisomers
ok i will move on. know the primary qn can liao, the molecule is chiral. hope u can elaborate on my above query if can
Thanks Ultima !
Which query? U posted 4 question marks. Choose 1 and I'll reply it. But NMR spec not in H2 syllabus lah, gao dim ur own syllabus first lah. -
what George chong meant regarding 2 hydrogens?
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Originally posted by Flying grenade:
what George chong meant regarding 2 hydrogens?
As for ur other query, the geometric isomerism of cycloalkanes is totally different from the geometric isomerism of cycloalkenes. The former involves the stereochemistry of 2 substituents on the ring, while the latter involves the stereochemistry of the double bond on the ring. -
Originally posted by UltimaOnline:
i thought the H in the OH functional group counts too thats why i thought there were 3 different types/environments !
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Originally posted by UltimaOnline:
As for ur other query, the geometric isomerism of cycloalkanes is totally different from the geometric isomerism of cycloalkenes. The former involves the stereochemistry of 2 substituents on the ring, while the latter involves the stereochemistry of the double bond on the ring.George Chong meant the 2 different 'types' (based on environments) of protium H atoms (ie. the 3 beta H atoms, and the alpha H atom), *excluding* the (alpha) deuterium H atom (written as D atom), in deuterated ethanol obtained when you use NaBD4 on ethanal.
okay i see. for cyclo alkanes, only substitutents exhibit cis trans only. for cycloalkenes, the whole molecule cis or trans about the double bond.
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Originally posted by Flying grenade:
okay i see. for cyclo alkanes, only substitutents exhibit cis trans only. for cycloalkenes, the whole molecule cis or trans about the double bond.
Of course, it's possible for cycloalkenes to have geometric isomerism for both the double bond as well as substituents. In which case (for A levels), u just need so specify whether the cis-trans isomerism refers to the substituents or the double bond, eg. "This molecule is cis in regard to the double bond, but trans in regard to the 2 Cl atoms on the ring". Cambridge won't require you to name such complicated molecules with more than 1 set of cis-trans isomerism present simultaneously. -
Originally posted by UltimaOnline:
Of course, it's possible for cycloalkenes to have geometric isomerism for both the double bond as well as substituents. In which case (for A levels), u just need so specify whether the cis-trans isomerism refers to the substituents or the double bond, eg. "This molecule is cis in regard to the double bond, but trans in regard to the 2 Cl atoms on the ring". Cambridge won't require you to name such complicated molecules with more than 1 set of cis-trans isomerism present simultaneously.ahh i seee !!! thank you 神!!!
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Originally posted by Flying grenade:
i thought the H in the OH functional group counts too thats why i thought there were 3 different types/environments !
Whether the OH group contains protium or deuterium, depends on the solvent (ie. H2O vs D2O).On a 2nd and closer read, it turns out George Chong meant distinguishing between the protium and deuterium as the 2 types of hydrogen atoms. Because the entire question is about why a C atom is considered chiral, when it's bonded to 2 H atoms, 1 protium and 1 deuterium.
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group 14 atom(Carbon) with unipositive formal charge and stable octet, impossible right?
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for a C atom in a carbocation intermediate , its just unipositive formal charge, with 3 bp around it right?
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Originally posted by Flying grenade:
group 14 atom(Carbon) with unipositive formal charge and stable octet, impossible right?
Yes. -
Originally posted by Flying grenade:
for a C atom in a carbocation intermediate , its just unipositive formal charge, with 3 bp around it right?
Yes. -
thx ultima
ethanedioic acid oxidise to carbonic(IV) acid before further decomposing?
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there's no methanal generated anywhere in the mechanism is it?
e.g. george chong organic book page 83
is it that the alkene is oxidised to ethanedioic acid then h2co3 then further to CO2 and H2O?
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Originally posted by Flying grenade:
thx ultima
ethanedioic acid oxidise to carbonic(IV) acid before further decomposing?
Yes. -
Originally posted by Flying grenade:
there's no methanal generated anywhere in the mechanism is it?
e.g. george chong organic book page 83
is it that the alkene is oxidised to ethanedioic acid then h2co3 then further to CO2 and H2O?
The CH2 side of a terminal alkene is oxidized to methanal which is further oxidized to methanoic acid which is further oxidized to carbonic acid which decomposes to CO2 and H2O, provided you heat under reflux with MNO4-/H+.