AS Chemistry P2 Prep.

[MiraiVi]

Jazak Allah Khayr.

Can someone please explain to me the reactions of KMnO4 on Alkenes?

Also, why does only KMnO4 show that kind of reaction with Alkenes; why doesn't K2Cr2O7, as they're both oxidizing agents?

On Cold, dilute KMnO4, Alkenes produce diols by the breakage of the Carbon-Carbon double bond.
On Hot, concentrated KMnO4, Alkenes produce Ketones, or aldehydes which on further oxidation produces carboxylic acids. (However Methanal on futher oxidation produces H2O and CO2)

I'm not sure why only KMnO4, but that is what is written in the syllabus, so that is what I follow I hope I helped

 

[floral123]

Jazak Allah Khayr.

Can someone please explain to me the reactions of KMnO4 on Alkenes?

Also, why does only KMnO4 show that kind of reaction with Alkenes; why doesn't K2Cr2O7, as they're both oxidizing agents?

JUST VISIT THIS LINK AND YOU ARE DONE!!!
http://www.chemguide.co.uk/organicprops/alkenes/kmno4.html

 

[angelgirl:)]

If the end of the molecule contains CH2 then CH2 is converted into H20 and CO2. The other side of the molecule must contain 2 bond, i.e CH and an other R group. The CH molecule is always converted into COOH. For eg, CH3-CH=CH2 = CH3COOH+CO2+H20.
Furhtermore there is a possibltiy that the left side of the molecule contains 2 R gps other than CH, if this happens then the resulting molecule is R-C-R with a double bond ketone oxygen group above oxygen. For e.g (CH3)2=CH2 = CH3_C(=O)-CH3+ Co2 + H2O

but the second eg is not clear...

 

[Saad (سعد)]

If the end of the molecule contains CH2 then CH2 is converted into H20 and CO2. The other side of the molecule must contain 2 bond, i.e CH and an other R group. The CH molecule is always converted into COOH. For eg, CH3-CH=CH2 = CH3COOH+CO2+H20.
Furhtermore there is a possibltiy that the left side of the molecule contains 2 R gps other than CH, if this happens then the resulting molecule is R-C-R with a double bond ketone oxygen group above oxygen. For e.g (CH3)2=CH2 = CH3_C(=O)-CH3+ Co2 + H2O

(CH3)2=CH2... you meant that to be this, right? (CH3)2C=CH2... so the CH2 at the end would turn into CO2 and H2O, and and the '(CH3)2C=' turns into a Ketone with 1 CH3 above the '=C=O' group and 1 below... is that right?

 

[angelgirl:)]

(CH3)2=CH2... you meant that to be this, right? (CH3)2C=CH2... so the CH2 at the end would turn into CO2 and H2O, and and the '(CH3)2C=' turns into a Ketone with 1 CH3 above the '=C=O' group and 1 below... is that right?

yes...

 

[angelgirl:)]

but its also important to concider where the double bond is present...as fom the double bond we will come to know about 1' ...2' and 3' alchole...and the produts they form with the oxidents...

 

[oldfashionedgirl]

Now, someone, please kindly, riddle me this.

Question 4, (f), (iii):

Paper: Click Me
Mark Scheme: No, Me!!!

... Why on planet Earth do those carbon atoms (in the mark scheme answer) have five bonds each?

lol, i think there gas been some misprinting in the mark scheme....i guess they forgot to remove the double bond even after addition of HBr

 

[Muhammad Ahmer Ali]

but the second eg is not clear...

OK take this example but this is a bit difficult
(CH3)2C=CHC6H5-----------------------CH3-C(=O)-CH3+C6H5COOH
In this example the reactant has a carbon atom containg 2 CH3 (R gps) on left side whereas on the other side there is a CH gp with C6H5....... So 2 R groups on left side are converted into a ketone namely propanone, and as on the right side there is CH group , COOH is formed and C6H5 as it is , the reulting 2nd molecule is C6H5COOH

 

[Saad (سعد)]

I think I get it now...

Now, the real challenge is not to forget. >.<

Thanks guys.

 

[alim]

wat are the conditions for substitution reaction of Hydrogen halide, phosphorus halide and SOCL2 in alcohol?

 

[angelgirl:)]

OK take this example but this is a bit difficult
(CH3)2C=CHC6H5-----------------------CH3-C(=O)-CH3+C6H5COOH
In this example the reactant has a carbon atom containg 2 CH3 (R gps) on left side whereas on the other side there is a CH gp with C6H5....... So 2 R groups on left side are converted into a ketone namely propanone, and as on the right side there is CH group , COOH is formed and C6H5 as it is , the reulting 2nd molecule is C6H5COOH

thanks..

 

[Muhammad Ahmer Ali]

wat are the conditions for substitution reaction of Hydrogen halide, phosphorus halide and SOCL2 in alcohol?

Just HEAT

 

[Saad (سعد)]

Another one; which way of writing equations is better;

2NO + 2CO --> 2CO2 + N2 ?

OR

NO + CO -->CO2 + 1/2N2?

I mean, is balancing the equations in fractions preferred in AS Level or in whole numbers?

 

[Muhammad Ahmer Ali]

Another one; which way of writing equations is better;

2NO + 2CO --> 2CO2 + N2 ?

OR

NO + CO -->CO2 + 1/2N2?

I mean, is balancing the equations in fractions preferred in AS Level or in whole numbers?

Both are acceptable but it is better to write in whole numbers

 

[Saad (سعد)]

Both are acceptable but it is better to write in whole numbers

Are you 100% sure? Because in the MS the Examiner gives almost always gives answers in fractions... that's why I asked...

 

[DragonCub]

wat are the conditions for substitution reaction of Hydrogen halide, phosphorus halide and SOCL2 in alcohol?

Just HEAT

Unless I am mistaken, SOCl2 and PCl5 don't need heating. They can perform substitution in under conditions.

 

[Muhammad Ahmer Ali]

Are you 100% sure? Because in the MS the Examiner gives almost always gives answers in fractions... that's why I asked...

Yeah there is no problem in it, I am writing this from childhood and never got a mark off......

 

[angelgirl:)]

Are you 100% sure? Because in the MS the Examiner gives almost always gives answers in fractions... that's why I asked...

ya both r acceptable...

 

[Muhammad Ahmer Ali]

Unless I am mistaken, SOCl2 and PCl5 don't need heating. They can perform substitution in under conditions.

Check nov 2006 p2 last question and the mark scheme you will get it then, even REFLUX can be used in this ......

 

[Pals_1010]

Does anyone know the syllabus for AS ?