A Level H2 Chemistry Tuition and notes Singapore

Protecting groups in organic chemistry

A protecting group or protective group is introduced into a molecule by chemical modification of a functional group to obtain chemoselectivity in a subsequent chemical reaction. It plays an important role in multistep organic synthesis.[1]

In many preparations of delicate organic compounds, some specific parts of their molecules cannot survive the required reagents or chemical environments. Then, these parts, or groups, must be protected. For example, lithium aluminium hydride is a highly reactive but useful reagent capable of reducing esters to alcohols. It will always react with carbonyl groups, and this cannot be discouraged by any means. When a reduction of an ester is required in the presence of a carbonyl, the attack of the hydride on the carbonyl has to be prevented. For example, the carbonyl is converted into an acetal, which does not react with hydrides. The acetal is then called a protecting group for the carbonyl. After the step involv…

Hi friends,
 Under these exceptional times, in case some of your are quarantined, here are some summary notes which I have found from internet for use during home based learning.
 They are in a zipped file. So just download from this link below and unzip the files and you are ready to use the notes.

 Keep safe!!

https://drive.google.com/open?id=176oOzxSs6PYcZPwLbpzeXUAJHM5aQXq1

Summary notes found from internet:

https://drive.google.com/open?id=1NE8M7SO9fxGMXdzH_6I2nJbIj3XK5Gz9
https://drive.google.com/open?id=1pm8Qnv61KvWiZ06J5xU3O4doCv-x6JpX
https://drive.google.com/open?id=1B7yOWIlnU4m3QSCDh5P6BPCU0NCHhJlP





Best regards,


Mr Chong

P / S online 1-1 interactive and live online tuition  is available from me.


Completely Compiled Chemistry for Singapore JC H2 syllabus by Chong56 on Scribd

Download file here : https://drive.google.com/open?id=1LqrgvNkw2BxqvNt7EbcYIP-sPU4V5UwH

Question : An organic compound X contains by mass, 63.2% carbon,
8.7% hydrogen, and 28.1% oxygen. On treatment with sodium
hydrogencarbonate solution, it liberates carbon dioxide. It also
undergoes an addition reaction with bromine in a 1:1 molar ratio
whereby 1.50 g of the compound reacts with 2.11 g of bromine.

(i) Calculate the empirical formula of X.

(ii) Calculate the relative molecular mass of X.

(iii) Determine the molecular formula of X.

Answer : Molecular formula of X is C6H10O2


Bonus question : 25.0 cm3 of a solution containing sodium hydroxide and sodium carbonate required
21.05 cm3 of 1 mol dm-3 HCl with phenolphthalein as indicator and a further 6.80 cm3of the same acid with methyl orange as indicator. Calculate the molar concentration of
each compound in the solution.

Ans:
conc of sodium carbonate = 0.272 mol dm-3

conc of sodium hydroxide = 0.570 moldm-3

When benzene reacts with 5-chloropentanoyl chloride in the presence of a catalyst, AlCl3, a few products are obtained. Suggest a likely organic product A.

Hi all,
 Some heterocyclic organic  compounds containing O, N or S atoms have appeared in 2019 H2 Chemistry Prelim Papers.

 So you may wish to read up on lactones, pyrroles or furans only if you have time.

You may search for "lactones" or "furans" or "pyrrole" in wikipedia.


All the best for your examinations!!

Signing off,
:)

Mr Chong

Novel organic chemistry reaction:

Read wikipedia on Diels Alder reaction:
https://en.wikipedia.org/wiki/Diels%E2%80%93Alder_reaction

Draw the structural formulas of A and B for the following reaction, given that A and B are constitutional isomers.

Question inspired  by Cambridge 2018 exam papers
By reading up on Wikipedia on Aldol reaction mechanism: https://en.wikipedia.org/wiki/Aldol_condensation#Mechanism Draw a possible product D of this reaction:

Hi all,
 There is a new book in Popular bookshops that is written by Mr Eric Kua. The title is "A Level Chemistry - Novel Organic Chemistry Questions".
 Why should you get a copy? It is for those who want to get a pass in your coming Prelims exams and a good grade in A levels Chemistry exams.
 What is it about? The guided questions are on novel Chemistry reactions and their mechanisms. These questions are likely to appear in prelims exams in one form or another. The standard of this book is around university year one / two organic chemistry. The author has provided lots of help and clues in the book.

 I shall heartily recommend this book.

See ya all and all the best!!

:)

Mr Chong

Here are questions and solutions from a merged JC taken from GCE A levels H2 Chemistry Prelim Paper 3.


H2 Chemistry Paper by Chong56 on ScribdSolutions for H2 Chemistry Paper by Chong56 on Scribd

Download the file here from Google Drive: https://drive.google.com/file/d/1boeekpDxkaPV18OgQ9E5Nk02PjB_a3iG/view?usp=sharing
Singapore-Cambridge GCE A l... by on Scribd

(As my website services are free, I regret that no answers are provided for this practice paper)

Download the practice paper here:

https://drive.google.com/open?id=1e3f3OrGE-hYSxCoV4FpQ2ZrucEeMAoyI


JC2 Chemistry Practice Paper - GCE A levels Chemistry 6092 by WesleyChong on Scribd

Chemical Equilibrium and Ionic Equilibrium tutorial by chong56 on Scribd

Organic Chemistry Tutorial by chong56 on Scribd

Download File from Google Drive here: https://drive.google.com/open?id=1gx5BH5umbrPqaIhX37WIQ4eZPVIgv-f3 Chemical Bonding Summary by chong56 on Scribd

Physical Chemistry Formulae List 2019 is available for download.

Download the file from Google Drive here:
https://drive.google.com/file/d/0B6cKG6RQCiyJTkxRM0FQUWMxRE0/view?usp=sharing

High School/ JC Chemistry Formulae List 2018 by chong56 on Scribd

Question : What are the Lewis structures of C3O, SCN- and (CN)2?

Polycyclic aromatic hydrocarbons consist of benzene rings fused together. 
Identify molecules A and B that can react in a one-step reaction to form the substituted Polycyclic Aromatic Hydrocarbon shown below.

Jc Practice Paper by chong56 on Scribd

Download the file here : https://drive.google.com/open?id=0B6cKG6RQCiyJR1RnOGN1V3RYYkE

1. Aluminium metal is widely used in countries worldwide. Aluminium has low density and strength that makes it ideal for construction of aircraft, lightweight vehicles, and ladders.

(a) [Chemical Bonding] Suggest with reference to the bonding why aluminium has higher melting point than sodium. [2]

(b) [Chemical Bonding] Aluminium compounds also have many uses in industries. Aluminium chloride, often in the form of derivatives, is a common component in antiperspirants, at low concentrations.
Draw the structure that aluminium chloride exists in vapour state. [1]
State the angle of Cl-Al-Cl in the above structure. [1]

(c) [Chemical Bonding] Aluminium chloride has a low melting point of 192.4 °C. Explain this phenomenon with reference to its bonding. [2]

(d) [Chemical Bonding] Draw the Lewis structure of the product when aluminium chloride reacts with nitrogen trifluoride, NF3 in a 1:1 mole ratio.[2]

(e) [Arenes] Friedal-Craft alkylation occurs when benzene reacts with chloroethane to fo…

Hi all,

 We are moving!! The blog web address has changed from http://alevelchemistrysg.blogspot.sg to http://www.alevelchemistrysg.com

 If you key in the old address http://alevelchemistrysg.blogspot.sg， you will still be redirected to the new web address.

 The contents of the blogs remain intact.

 Thank you for your kind attention!!

Mr Chong
Chemistry tutor

Organic chemistry – Question on reaction mechanism

The above reaction is known as the mechanism of Kolbe reaction. (a)Name 2 types of reaction in the mechanism. (b)Write an overall equation consisting of 2 stages to represent the mechanism. Sulfuric acid is used in the last stage of the reaction. (c)Suggest a solvent to carry out the reaction.

Mock questions for JC2 Prelims Practice Paper Basic Questions for JC2 Practice Paper by ABC

Download  Mock questions for JC2 Prelims Practice Paper for free here.

Organic Chemistry Structural Elucidation Question by ABC

A level Chemistry Practice Questions by ABC

Similar substances have appeared in recent Cambridge papers.
Do you think teachers will prefer these substances this year?




































Can you spot enol-keto tautomers, anhydrides, peroxy acid, amide, epoxide, sodium superoxide? Teachers may like sodium peroxide too.

 2019 may see different types of molecules appearing as Cambridge may have younger professors who are so brilliant, to set the papers for the new syllabus.

Related links to these molecules: