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In today's lecture, we revised about halogenoalkanes. They have quite a number of reactions which sometimes I still get mixed up on. We also learnt about the 2 types of nucleophilic substitutions and how it differs from each other. The lecture also refreshed my memory about the mechanisms of the reactions and how to draw the curly arrow diagrams.

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In this lecture I was able to revise about alkanes and its reactions of nucleophilic substitution. I revised about SN1 and SN2  reactions. SN1 is for tertiary carbocations and has two steps of reactions which forms an intermediate while SN2 is for primary carbocations and has one step. I also revised about elimination reactions.

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Today we revised the definition of halogenalkanes, nucleophilic subsitution (reactions with KCN and ammonia) and the different nucleophiles in each reaction (OH in  NaOH and HCl and water, KCN in ethanol, excess in ammonia, aqueous silver nitrate all heated in reflux). We also revised SN1 and SN2 mechanisms; that SN1 for tertiary and secondary molecules has 2 steps and forming carbocations and SN2 for secondary and primary molecules has 1 step and forms the intermediate - this is reflected in the graph, where SN1 reactions have two activation energies while SN2 reactions have only one. We also stressed on the importance of the colours of the compounds AgCl (white), AgBr (cream) and AgI (yellow).

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I reviewed on the reactions of halogenoalkanes (nucleophilic substitution) and its mechanism (SN1 and SN2). I learned that reaction with hydrolysis is slower than reaction with NaOH due to the OH- ion. SN1 forms carbocations, while SN2 forms intermediate. I also learned elimination reaction using NaOH in ethanol and poly(alkene) is difficult to be disposed of in non-biodegradable. I need to review more on the curly arrow diagram. Overall, today’s lecture is very helpful for reviewing about halogenoalkane.

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I recalled the different nucleophilic substitution reactions : aq NaOH / aq AgNO3 and it’s differences, CN reaction and NH3 reaction, and elimination. I also recalled the SN1 (tertiary halogenoalkane) and SN2 (primary halogenoalkane) reactions and how to draw them.

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the lecture helps me remember about the reaction of halogenoalkanes (nucleophilic substitution) with NaOH (reflux), KCN (ethanolic, reflux), and NH3 (excess, ethanolic, under pressure). it also helps me remembering the mechanism, SN1 (tertiary and secondary) and SN2 (primary and secondary). the pyp questions were very helpful!

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Today I reviewed about
- halogenoalkanes
- nucleophilic substitution (KCN/Ammonia)
- Difference between water and OH as nucleophile
- SN1/SN2 mechanism
- Elimination reaction
- polyalkene

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Today i learned:

1) What a halogenoalkane is.

2) What a nucleophile is.

3) Nucleophilic substitution reactions with its conditions and nucleophile involved [Aqueous alkali (heated under reflux), KCN in ethanol (heated under reflux), Excess ammonia in ethanol (heated under pressure), Aqueous AgNO3 (heated under reflux)]

4) Colour of AgBr, AgCl, AgI ppt.

5) SN1 (secondary and tertiary, forms carbocation) and SN2 (secondary and primary, forms an intermediate)

6) How to draw the mechanism for SN1 (2 step, slow -> fast) and SN2 (1 step) nucleophilic substitution.

7) SN1 have 2 humps on an energy/progress of reaction graph.

8) Elimination reaction [alkali in ethanol (heated under reflux)]

9) Poly(alkene) is difficult to be disposed of because it is non-biodegradable/non-reactive because of its saturated bond/cannot be broken down/release toxic gas.

Very good lecture 👌

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Today we reviewed about the halogenoaklkanes chapter but most importantly free radical substitution, electrophilic addition, nucleophilic addition and nucleophilic substitution. We also revised about the definition of nucleophiles which are electron donors. We also revised about the Sn1 and Sn2 Mechanisms and that sn1 reacts with tertiary carbocations and sn2 reacts with primary carbocations. we also revised that sn1 form carbocations and sn2 forms intermediate. When reactiong in order for ammonia not be fought back we need excess in nucleophilic substitution.

I need to revise on the curly diagrams more and also memorize the conditions.

Overall today's lesson was super informative as always and was very clear and easy to understand.

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Revised :
- free radical substitution
- electrophilic addition
- nucleophilic addition
- nucleophilic substitution
- nucleophiles are electron donors
- hydrolysis happens slower than sodium hydroxide —> due to the OH- ion
- revised on the curly arrow diagrams for SN1 and SN2
- SN1 —> forms carbocations
- SN2 —> forms intermediate
- elimination reaction —> NaOH in ethanol
- nucleophilic substitution needs excess ammonia in ethanol to prevent further formation of mixed products

I need to revise on the curly arrow diagram’s mechanism as I often forget about its mechanism

Overall, Mr Gopi’s teaching has served as a quick revision to me ; very helpful and informative

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we reviewed about halogenoalkanes and the different types of mechanism as well as the Sn 1 and Sn2 mechanisms. For Sn 1 mechanisms, tertiary carbocations will undergo Sn 1 and form carbocations because they are relatively stable and have a more positive conducting effect compared to primary carbocations and for Sn2, primary carbocations will undergo Sn1 and form a  intermediate due to its unstable nature and repulsion between nucleophiles will occur removing the nucleophile and lastly a carbocation is formed. Overall, the lecture was informative and fun

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from lecture day 1, Mr Gopi opened up my eyes and mind when approaching chemistry in general. thank you sir for letting me participate in your lecture sessions, it was truly an honor. ur teaching skills are very impressive and the way that you covered so many subtopics in just an hour is truly amazing, hope to see you in person haha :)

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Very smooth flow of teaching. Good use of real life examples and terminologies. Very useful for revision.

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Very smooth flow of teaching. Good use of real life examples and terminologies. Very useful for revision.

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Clarence BDGS

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We reviewed about halogenoalkanes and the different reactions, like nucleophilic addition, etc. I also learned about the Sn1 and Sn2 reactions, where Sn1 produces carbocation and Sn2 produces intermediate. The lesson was easy to grasp and I was able to fully understand it.

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A very thorough revision on the halogenoalkanes topic. Re-discussed about both the SN1 and SN2 mechanisms, as well as the nucleophilic reactions as well. All his explanations are clear and easy to understand.

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I love his teaching style. I understood everything even the things I still have doubts on previously. Keep going!!

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I remember about different type of reaction :

Nucleophilic substitution
1. NaOH (aq) alkali - reflux
2. KCN in ethanol - reflux
3. Excess Ammonia in ethanol - under pressure

AgNO3 (heated under reflux)

Comparing NaOH (aq) & AgNO3 (aq)
NaOH :
- Reflux
- Alcohol
- OH-
- Fast
- No ppt

AgNO3 (aq)
- Reflux
- Alcohol
- H2O
- Slow
- Have precipitation

KCN in ethanol (under reflux)
- Do NOT confuse wity Carbonyl compund (+HCN) [made from NaCN + H2SO4]

Review :
SN1 - Tertiary alcohol (more stable) (more positive inductive effect) - carbocation
SN2 - Primary alcohol  - Intermediate

SN2 :
- Curly arrow

SN1 :
- Curly arrow
- Two step (slow , fast)

Elimination reaction :
- NaOH in ethanol / ethanolic sodium hydroxide + reflux

Need more practice :
- Drawing curly arrows
- Naming products
- Memorize conditions

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Fully reminded on Sn1 and Sn2 nucleophilic substitution and a lot more. A fresh reminder on the halogenoalkanes chapter.

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A good revision about halogenoalkanes and their reactions along with their reactions. The past paper questions really helps to show how to answer questions related with the topic

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One of the best teaching styles i’ve encountered

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One of the best teaching styles i’ve encountered

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Covers all the necessary requirements of our syllabus, including very nice analogies easy to grasp.

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it was very comprehensive

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Mr Gopi refreshed my memory about the mechanism. i fully understood his explaination.