The Umbrella Academy

The Umbrella Academy

Free Online Academy of Physical and Chemical Sciences

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Is Methane (CH4) really tetrahedral? 09/06/2023

Is Methane (CH4) really tetrahedral? This lecture describes how chemists came to know that methane has a tetrahedral structure. The lecture takes you through various possible structures one can ...

Baeyer Villiger Oxidation/ Rearrangement 13/05/2023

The transformation of ketones into esters and cyclic ketones into lactones by peroxyacids is called Baeyer-Villiger oxidation or Rearrangement. In case of unsymmetrical ketones, different groups migrate at different rates depending on their ability to stabilize the transition state. The migrating group migrates with retention of configuration.

Baeyer Villiger Oxidation/ Rearrangement The transformation of ketones into esters and cyclic ketones into lactones by peroxyacids is called Baeyer-Villiger oxidation or Rearrangement. In case of ...

Enamine: Formation, properties and Reactivity 24/04/2023

This lecture describes the formation of enamines by reaction of carbonyls with secondary amines. The mechanism is similar to Imine formation except that last deprotonation occurs at carbon since iminium ion doesn't contain any hydrogen attached to nitrogen.
Enamines beta carbon is more basic than its nitrogen due to pi donation by nitrogen lone pair into alkene pi bond. Enamine nitrogen is less basic than nitrogen of corresponding amine. Overall enamine is more basic than corresponding amine. And because of this basicity enamine shows many reactions at beta carbon with electrophiles like alkylation, conjugate addition and cross Aldol reaction etc.

Enamine: Formation, properties and Reactivity This lecture describes the formation of enamines by reaction of carbonyls with secondary amines. The mechanism is similar to Imine formation except that last...

Wolff-Kishner reduction 23/03/2023

Reduction of carbonyl group of aldehydes and ketones to methylene group by heating their hydrazones or semi-carbazones in the presence of a strong base such as KOH or t-BuOK in ethylene glycol or DMSO solvent. Semi-carbazones are first hydrolyzed to hydrazones before reduction is attempted.

Wolff-Kishner reduction Reduction of carbonyl group of aldehydes and ketones to methylene group by heating their hydrazones or semi-carbazones in the presence of a strong base such ...

Formation of Imine: Properties and Mechanism 01/03/2023

Imines are the nitrogen analogs of Aldehydes and ketones, that contain a C=N double bond, instead of a C=O double bond. Imines are also called Schiff bases, named after Hugo Schiff, a German chemist who first described their formation. Other ammonia derivatives such as hydroxyl amine and hydrazine, also react with aldehydes and ketones, to give imine products. Oximes, semicarbazones, and phenyl hydrazones are often solid compounds with characteristic melting points. Standard tables give the melting points of these derivatives for thousands of different ketones and aldehydes.
If an unknown compound forms one of these derivatives, the melting point can be compared with that in the table. If the compound’s physical properties match those of a known compound and the melting point of its oxime, semicarbazone, or phenylhydrazone matches as well, we can be fairly certain of a correct identification.

Formation of Imine: Properties and Mechanism Imines are the nitrogen analogs of Aldehydes and ketones, that contain a C=N double bond, instead of a C=O double bond. Imines are also called Schiff bases,...

Cannizzaro Reaction 21/02/2023

When reacted with concentrated NaOH or other strong bases (e.g., alkoxides), aliphatic and aromatic aldehydes with no α-hydrogen undergo an intermolecular hydride-transfer reaction known as the Cannizzaro reaction. In this disproportionation reaction, one molecule of aldehyde oxidizes another to the corresponding carboxylic acid and is reduced to the corresponding primary alcohol. If the aldehyde has α-hydrogens, the aldol reaction will take place faster than the Cannizzaro reaction. Cross Cannizaro Reaction occurs between two different non enolizable aldehydes. Mostly one aldehyde is Formaldehyde. α-Keto aldehydes undergo an intramolecular Cannizzaro reaction.

Cannizzaro Reaction When reacted with concentrated NaOH or other strong bases (e.g., alkoxides), aliphatic and aromatic aldehydes with no α-hydrogen undergo an intermolecular hy...

Benzoin Condensation 12/02/2023

https://youtu.be/m8Zf_CNucp8
Upon treating certain (but not all) aromatic aldehydes or glyoxals (α-keto aldehydes) with cyanide ion (CN-), benzoins
(α-hydroxy-ketones or acyloins) are produced in a reaction called the benzoin condensation. One of the aldehydes serves as the
donor and the other serves as the acceptor. Some aldehydes can only be donors (e.g. pdimethylaminobenzaldehyde)
or acceptors, so they are not able to self-condense, while other aldehydes
(benzaldehyde) can perform both functions and are capable of self-condensation. All the steps of the cyanide ion catalyzed benzoin condensation are completely reversible.
The cyanide ion is a very specific catalyst of the reaction. Cyanide is a good nucleophile, a good leaving group, and its electron withdrawing effect enhances the acidity of the aldehyde hydrogen.

Benzoin Condensation Upon treating certain (but not all) aromatic aldehydes or glyoxals (α-keto aldehydes) with cyanide ion (CN-), benzoins(α-hydroxy-ketones or acyloins) are pro...

Shortcut method for Aldol Reaction product. 05/02/2023

https://www.youtube.com/watch?v=Z_wsy1wCQpk
This lecture describes a short cut method to write the product of Aldol reaction directly without going through tedious mechanism. The lecture also describes the method of finding the starting reagents that had formed a particular Aldol Product.

Shortcut method for Aldol Reaction product. This lecture describes a short cut method to write the product of Aldol reaction directly without going through tedious mechanism. The lecture also describes...

ENOLATE CHEMISTRY; FORMATION & STABILITY, KINETIC VS THERMODYNAMIC 22/01/2023

https://youtu.be/AuMOUsQX27U
The α-carbon of carbonyls, especially Aldehydes and ketones, can be deprotonated by a base to form carbanion which is resonance stabilized by carbonyl group to form enolates. These are important reaction intermediates. Unsymmetrical ketones can give two different enolates called Kinetic enolate (formed faster by abstraction of less hindered α-proton) and thermodynamic enolate (formed slowly by abstraction of more hindered proton). Thermodynamic enolate is more stable and hence dominates at equilibrium. Kinetic enolates can be formed selectively by using strong bulky base like LDA. Enolates are nucleophiles and undergo reaction with electrophiles.

ENOLATE CHEMISTRY; FORMATION & STABILITY, KINETIC VS THERMODYNAMIC The α-carbon of carbonyls, especially Aldehydes and ketones, can be deprotonated by a base to form carbanion which is resonance stabilized by carbonyl group ...

10/07/2022

Eid Mubarak...

Ozonolysis of Alkenes 12/06/2022

Ozonolysis converts alkene double bonds into ozonide which upon reduction with mild reducing agent like dimethylsulfide converts double bonded carbons into carbonyl groups. Thus unlike treatment with osmium tetraoxide or cold Dilute KMnO4 or epoxidation followed by acid catalyzed ring opening, where only pi bond is oxidized so that both double bonded carbons are hydroxylated to form glycol, in this case both pi as well as sigma bond is oxidized.
The formation of products under different conditions is explained using various examples.
https://youtu.be/eiZYj3lwIAg

Ozonolysis of Alkenes This lecture describes the oxidative cleavage of alkenes by Hot conc. KMnO4 and Ozonolysis followed by reduction with mild reducing agent like dimethylsulfid...

Syn Dihydroxylation of Alkenes with OsO4 and KMnO4 04/06/2022

Syn dihyroxylation of alkenes is achieved with either Osmium tetraoxide or potassium permangnate. OsO4 is expensive but gives better yield whereas KMnO4 is cheap but gives lower yield. OsO4 is therefore used along with co-oxidant which regenerates the reagent and is therefore needed in catalytic amounts. Typical co-oxidant are NMO and t-butylhydropoeroxide. The choice of reagent for syn dihyroxylation depends on the circumstances.

https://youtu.be/QZFD-rEXYOM

Syn Dihydroxylation of Alkenes with OsO4 and KMnO4 This lecture describes the reagents used for achieving Syn dihydroxylation of alkene double bonds. The advantages and disadvantages of Osmium tetroxide and P...

Epoxidation of Alkenes; Trans Dihydroxylation of Alkenes 20/05/2022

Dihydroxylation reactions are characterized by the addition of OH and OH across an alkene. A two-step procedure for anti dihydroxylation involves conversion of an alkene to an epoxide (also called oxirane), followed by acid-catalyzed ring opening. The result is the formation of trans diol, called glycol. Anti Dihydroxyaltion of Cis-2-butene gives a pair of enantiomers whereas that of trans-2-butene gives a single meso product, just like halogenation reaction.
https://www.youtube.com/watch?v=_tUE1r4B228

Epoxidation of Alkenes; Trans Dihydroxylation of Alkenes Dihydroxylation reactions are characterized by the addition of OH and OH across an alkene. A two-step procedure for anti dihydroxylation involves conversion ...

Halohydrin formation from Alkenes 10/05/2022

The difference between halogenation of alkenes and halohydrin formation is that later is Regioselective because two different groups are added across alkene. The bromonium ion intermediate is captured and opened by water (or any other nucleophile/solvent) to form oxonium ion which is deprotonated to form halohydrin. The reaction is stereospecific as only anti enantiomers are formed.

https://www.youtube.com/watch?v=48tH9L3Epnc

Halohydrin formation from Alkenes The difference between halogenation and halohydrin formation of alkenes is that later is Regioselective because two different groups are added across alkene....

Stereochemistry of Halogenation of Alkenes 06/05/2022

Halogenation of alkenes is stereospecific, different starting material give different products. Cis-2-butene on Halogenation gives enantiomeric (+-)2,3-dibromobutane as product whereas trans-2-butene on Halogenation gives single (meso)2,3-dibromobutane as product. The mechanism for this stereospecificity is explained in this lecture.

https://youtu.be/TDrohmVuIak

Stereochemistry of Halogenation of Alkenes This lecture describes the mechanism of halogenation of alkenes. Halogenation is stereospecific reaction that is different starting material give different p...

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