A Level H2 Chemistry Tuition and notes Singapore

A nucleophilic aromatic substitution is a substitution reaction in organic chemistry in which the nucleophile displaces a good leaving group, such as a halide, on an aromatic ring. This is an unusual reaction for H2 Chemistry students because electrophilic aromatic substitution is usually encountered for arenes.
 An example: SNAr mechanism:

In the mechanism, electron withdrawing groups activate the ring towards nucleophilic attack, for example if there are nitro functional groups positioned ortho or para to the halide leaving group.
Explain which mechanism will yield the fastest rate given that the nucleophile is methoxide ion, CH3O-, and the each of the substrates are given below. Draw the organic products that are formed.

How do you convert butanoic acid to 2-pentanone in less than 6 steps?You may need to use a Grignard reagent. Grignard reagent has appeared in prelim papers before. Read about Grignard reagents on wikipedia.https://en.wikipedia.org/wiki/Grignard_reaction

2017 Singapore H2 Chemistry Prelim papers by Chong56 on Scribd

In the chapter of electrochemistry, the Nernst equation is in the grey area of the syllabus.
So let us look briefly at what is the Nernst equation.

Understanding the Nernst Equation The Nernst equation finds the cell potential of a reaction, or how much "power" a reaction will have at any given moment. You can use the equation to find out how much juice is in your battery.
Below is the general formula for the Nernst equation. You'll need to refer to it again when we perform our sample calculations.
You may be wondering what all those letters in the equation mean. To decipher them, take a look at the key below:
E: refers to the cell potential, or the amount of voltage, the reaction will have under set conditions. Eo: refers to the cell potential, or voltage, the reaction will have under set-standard conditions. R: refers to the ideal gas constant, which is 8.314 J/mol-K. T: refers to the temperature in Kelvins (K); room temperature equals 298 K. n: refers to the num…

Free-radical polymerization is a method of polymerization by which a polymer forms by the successive addition of free-radical building blocks. Free radicals can be formed by a number of different mechanisms, usually involving separate initiator molecules. Following its generation, the initiating free radical adds monomer units, thereby growing the polymer chain.



 Illustrate the first two steps of the mechanism when the monomer is ethene and the initiator molecule is dicumyl peroxide.

Pinacol Rearrangement

The pinacol rearrangement was the first molecular rearrangement identified as such by early chemists. The defining example of a pinacol rearrangement is shown in the following diagram.
As shown in the mechanism, from the initial diol, there is a shift of a methyl group to an adjacent carbon, and a carbonyl group is produced in the final step of the mechanism.








Predict the product when the following molecule undergoes pinacol rearrangement:

Download the file here:

https://drive.google.com/file/d/1G14u-v0Kj1XEZCpGHZwB71njKgtFS3H-/view?usp=sharing

The E1 mechanism involves the elimination of a molecule HBr from the alkyl halide to form an alkene. It is a first order reaction.
The mechanism is as shown:




Suggest how the kinetics of the reaction is affected as a stronger base is used, such as the ethoxide ion, CH3CH2O-, instead of hydroxide ion.
Why might carbocation rearrangement sometimes occur in E1 reaction?

Hi, there are 24 pages of challenging questions and solutions.

Download file here:

https://drive.google.com/file/d/1A-GEKvpEVHiCeOx5s2xRLUjvzMvmar5b/view?usp=sharing

Sample :

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

https://drive.google.com/file/d/1aIi2VtWrFnYhrEEjZRk4nsAOOv4cf7OJ/view?usp=sharing





Best regards,


Mr Chong

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



JC H2 Chemistry Summary not... by Chong56 on Scribd
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.