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Hammond’s postulate  (or the Hammond-Leffler postulate ) helps us predict whether a transition state ( TS ) may be reactant-like or product-like (or something else) in an exothermic/endothermic reaction. If we consider potential energy diagrams (reaction profiles), it’s well understood. Click/tap to enlarge the images TS = Transition state RDS = Rate-determining step Do you like energy diagrams❓ Let Chemaficionado know in the comments below or at mychemistryhomework@gmail.com ❗ References: (1)      Wikipedia Contributors.  Hammond’s postulate . Wikipedia. ‌ (2)      Chouhan, M. S.  Advanced Problems in Organic Chemistry for JEE , 11th Ed .

The rotational free energy barrier depends on the bond’s ability to rotate. Less steric crowding  & no partial/complete double bond character lower the rotational energy barrier. A free rotation is not allowed around a double bond; else, it would break the  π─ bond.   Question: Arrange the following compounds in the increasing order of their C-C bond rotations: Click to enlarge the image Solution infographic: Click to enlarge the image How is it❓ Let Chemaficionado know at mychemistryhomework@gmail.com ❗ References: (1)      Wikipedia Contributors. Aromaticity. Wikipedia. https://en.wikipedia.org/wiki/Aromaticity. (2)      Wikipedia Contributors.  Resonance (chemistry) . Wikipedia. https://en.wikipedia.org/wiki/Resonance_(chemistry). (3)      Chouhan, M. S.  Advanced Problems in Organic Chemistry for JEE , 11th Ed.

The gas chromatography-mass spectrometry (GC-MS) electron ionization (EI) may also result in ortho - rearrangement . The same requirements for McLafferty rearrangement apply to ortho - rearrangement except for the strong α,β- C=C double bond. ortho - rearrangement, which initiates charge-site reaction, resulting in the loss of a small neutral molecule (water, HCl or the like), can be utilized to differentiate ortho - from para - and meta - isomers. This reaction is also observed for three unsaturated functional groups, viz ., thioesters, esters and amides. Tropylium ion is formed due to a rearrangement from a molecule having a benzyl (PhCH 2 -) group, such as, o -Toluic acid as shown in the image below. Click to enlarge the image M = Molecular, OE = Odd-electron, EE = Even-electron Is the infographic easy to comprehend❓ Let Chemaficionado know at mychemistryhomework@gmail.com ❗ References: (1)      Wikipedia Contributors.  Mass spectral interpretation ....

Considering neutral loss from the molecular ion or a fragment/product ion in mass spectrometry ? As a general rule, loss of 3 to 14 or 21 to 26 is not reasonable in the gas chromatography-mass spectrometry (GC-MS) electron ionization (EI) . These are likely to be formed from noise spikes or ions from an impurity. However, look at the GC-MS EI spectrum of 4,4-Dimethylcyclohexene! Click to enlarge the image M = Molecular Is the infographic easy to understand❓ Let Chemaficionado know at mychemistryhomework@gmail.com ❗ References: (1)      Varian Saturn GC/MS Mass Spectral Interpretation Quick Reference Guide. (2)      National Institute of Standards and Technology.  NIST Chemistry WebBook - SRD 69 . NIST. https://webbook.nist.gov/chemistry/.

The mighty Mitsunobu reactions ! The Mitsunobu reaction (or Mitsunobu displacement ) mechanism is complicated but related to the (aliphatic) nucleophilic substitution (S N 2) (inter- and intramolecular) and can convert alcohols into various products using different nucleophiles (Nu) (mildly acidic) . EWG-N=N-EWG may be DEAD (Diethyl azodicarboxylate). Wheel of Mitsunobu reactions: Click/tap to enlarge the image Nu (on the infographic ): Nucleophiles , pKa < 13 Alkanes Carboxylic acids Phenols, alcohols Thiols, Thioacetic acid/thiols/aryl mercaptans Secondary amine,  N -( tert -Butoxycarbonyl)-4-toluenesulfonamide/ EWG 2 NH /Thalimide Hydrazoic acid Zinc halide Inversion of configuration takes place if an ester is formed using the Mitsunobu reaction while retention of stereochemistry occurs if an ester is formed using the Fischer-Speier esterification or Fischer esterification . What other wheel(s) 🎡 of organic reactions would you like to see❓ Questions ❓ Let Chemaficion...

It may sometimes look like there exists a correlation between the optical rotation & the absolute configuration . However, the optical rotation is NOT directly related to the absolute configuration. Click/tap to enlarge the image S N 2 = Substitution nucleophilic bimolecular Does it make sense❓ Let Chemaficionado know in the comments below or at mychemistryhomework@gmail.com ❗ References: (1)      Wikipedia Contributors.  Cahn–Ingold–Prelog priority rules . Wikipedia. https://en.wikipedia.org/wiki/Cahn%E2%80%93Ingold%E2%80%93Prelog_priority_rule s. (2) Chouhan, M. S.  Advanced Problems in Organic Chemistry for JEE , 11th Ed.

The intermediate stability is one of the most important aspects in any organic reaction. The stability due to some electronic effects matters. Question: Which one of the two in the following pairs shows greater reactivity toward AgNO 3 or hydrolysis? Click to enlarge the image Solution infographic: Click to enlarge the image I effect = Inductive effect Liked the explanation❓ Let Chemaficionado know at mychemistryhomework@gmail.com ❗ References: (1)      Carbocation . Wikipedia. https://en.wikipedia.org/wiki/Carbocation. (2)      Wikipedia Contributors. Aromaticity . Wikipedia. https://en.wikipedia.org/wiki/Aromaticity. (3)      Inductive effect . Wikipedia. https://en.wikipedia.org/wiki/Inductive_effect. (4)    Wikipedia Contributors.  Resonance (chemistry) . Wikipedia. https://en.wikipedia.org/wiki/Resonance_(chemistry). (5)     Chouhan, M. S.  Advanced Problems in Organic Chemistry for JEE , ...

An ambient ion has multiple nucleophilic sites; and therefore, is likely to produce multiple products! A nucleophilic site has a negative charge or a lone pair of electrons. Question: Predict the product(s) of the following reaction: Click to enlarge the image Solution infographic: Click to enlarge the image The above is an S N 2 (substitution nucleophilic bimolecular) reaction. Want more about ambient ions❓ Let Chemaficionado know at mychemistryhomework@gmail.com ❗ Reference: Wikipedia Contributors.  Phenolates . Wikipedia .

The retro-Diels–Alder (rDA) reaction is the reverse of the Diels–Alder (DA) reaction , a [4+2] cycloelimination. For cyclohexene derivatives, the π -electrons are excited and generate a charge site and a radical site upon gas chromatography-mass spectrometry (GC-MS) electron ionization (EI) . It undergoes an rDA rearrangement to give diene and alkene (dienophile) fragment/product ions via two successive α -cleavages. The charge may be retained by either fragment as evident from the spectrum. This rearrangement may occur by a radical or an ionic mechanism. Click to enlarge the image M = Molecular, EE = Even-electron, OE = Odd-electron Is the infographic easy to grok❓ Let Chemaficionado know at mychemistryhomework@gmail.com ❗ References: (1)      Wikipedia Contributors.  Retro-Diels–Alder reaction . Wikipedia. (2)      National Institute of Standards and Technology.  NIST Chemistry WebBook - SRD 69 . NIST. https://webbook.nist.gov/c...

Rearrangement mechanisms in chemistry are fascinating, aren't they? The McLafferty rearrangement , which may occur by a radical or an ionic mechanism, is observed in the gas chromatography-mass spectrometry (GC-MS) electron ionization (EI) during the dissociation of organic molecules containing a carbonyl-group and at least one γ -hydrogen atom, which involves a β -cleavage. For methyl esters, say, a fragment/product ion with an m/z = 74 is seen in the GC-MS EI spectrum. Here you go - A double McLafferty (like) rearrangement! Click to enlarge the image M = Molecular, EE = Even-electron, OE = Odd-electron Is the infographic easy to understand❓ Let Chemaficionado know at mychemistryhomework@gmail.com ❗ References: (1)      Wikipedia Contributors.  McLafferty rearrangement . Wikipedia. (2)       SDBS, Spectral Database for Organic Compounds, AIST . sdbs.db.aist.go.jp. https://sdbs.db.aist.go.jp/.

Is it necessary that a strong-field ligand (SFL) causes electron-pairing ? Spectrochemical series (in the increasing order of the ligand-field strength): I −  < B r −  < S 2−  < S CN −  < C l −  < N O 3 −  < N 3 −  < F −  < O H −  < C 2 O 4 2−  < O 2−  < H 2 O < N CS −  < C H 3 CN < E DTA 4- < p y < N H 3  < e n < b ipy < p hen < N O 2 −  < P Ph 3  < C N −  < C O py = Pyridine, en = Ethylenediamine, bipy = 2,2'-Bipyridine, phen = 1,10-Phenanthroline, PPh 3 = Triphenylphosphine Mnemonic :   I Br ing S ome S weet C hocolate N ice N uts F or O ur C ute O ptimistic H appy N aughty C hildren E ffortlessly, P erhaps N ot E nough, B ut P al, N o P roblem C aring C ubs Question: Which of the following ions will form an inner orbital complex? Which one(s) will form an outer orbital complex? [Co(NH 3 ) 6 ] 3+ , [Ni(NH 3 ) 6 ] 2+ , [Ni(...

The standard  atomic weight is the weighted average (arithmetic mean) mass of the element; so, it's never an integer! Isotopes are distinct nuclides (or nuclear species) of the same chemical element, E and have the same atomic number, Z (number of protons, p in their nuclei), but different nucleon numbers (mass numbers, A ) due to different numbers of neutrons, n in their nuclei. Question: The standard atomic weight of Sr is 87.62 . Given that there are only three naturally occurring isotopes of strontium, 86 Sr, 87 Sr, and 88 Sr , which one is the most abundant isotope? Solution: Click/tap to enlarge the image How is it ❓ Let Chemaficionado know  in the comments below or at mychemistryhomework@gmail.com ❗ References: (1)      Wikipedia Contributors.  Standard atomic weight . Wikipedia . (2)      Wikipedia Contributors. Isotope . Wikipedia. https://en.wikipedia.org/wiki/Isotope.

How to decide on aromaticity ? Aromaticity is a chemical property in which a conjugated ring of unsaturated bonds, lone pairs ( lp ), or empty orbitals exhibits a stabilization greater than would be expected from conjugation alone.  Hückel's rule   helps predict aromaticity albeit with limitations. The  infographic below explains (hopefully): Click/tap to enlarge the image lp = Lone pair Is it coherent ❓ Let Chemaficionado know  in the comments below or at mychemistryhomework@gmail.com ❗ References: (1) Wikipedia Contributors. Aromaticity . Wikipedia. https://en.wikipedia.org/wiki/Aromaticity. (2) Wikipedia Contributors. Hückel’s rule . Wikipedia.

Does resonance necessarily lead to a decrease in basicity ? Resonance or delocalization of electrons typically reduces the basicity of an organic compound since basicity means an ability to donate an electron pair according to Lewis. But… Question: Explain why Acetamide is neutral while aqueous solutions of Guanidine are nearly as basic as those of Sodium hydroxide.   Solution infographic: Click/tap to enlarge the image EN = Electronegative, cA = Conjugate acid Does it add up ❓ Let Chemaficionado know  in the comments below or at mychemistryhomework@gmail.com ❗ References: (1)      Wikipedia Contributors.  Resonance (chemistry) . Wikipedia. https://en.wikipedia.org/wiki/Resonance_(chemistry). (2)      Acetamide . Wikipedia. https://en.wikipedia.org/wiki/Acetamide. (3)      Guanidine . Wikipedia. https://en.wikipedia.org/wiki/Guanidine.

Regiochemistry is reagent dependent! Alcohol dehydration (loss of water) is an important reaction in organic chemistry as it opens the possibility of numerous derivatives. Question: Predict the major products A , B , C of the following reactions: Click/tap to enlarge the image Solution infographic: Click/tap to enlarge the image E1 = Elimination unimolecular, E2 = Elimination bimolecular Does it make sense ❓ Let Chemaficionado know in the comments below or at mychemistryhomework@gmail.com ❗ References: (1)      Wikipedia Contributors.  Zaytsev’s rule . Wikipedi a. (2)      Rearrangement reaction . Wikipedia. https://en.wikipedia.org/wiki/Rearrangement_reaction. (3)      Wikipedia Contributors.  Elimination reaction . Wikipedia.