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In a nucleophilic aromatic substitution ( NAS or S N Ar ) the nucleophile displaces a good leaving group, viz ., a halide, on an aromatic ring. Aromatic rings are usually nucleophilic, but some aromatic compounds do undergo nucleophilic substitution especially if o-,p -positions carry strong electron withdrawing groups ( EWGs ). One such NAS takes place via addition-elimination mechanism that makes use of the Meisenheimer complex . Wheel of NAS by addition-elimination: Click/tap to enlarge the image Reagents -> Products (on the infographic ): 1 . Sodium hydroxide,  Δ 2 . Acid workup-> o-,p- substituted phenol Sodium methoxide,  Δ  ->  o-,p- substituted anisole Potassium phenoxide,  Δ  ->  o-,p- substituted diphenyl ether Sodium disulfide,  Δ  ->  o-,p- substituted diphenyl disulfide Sodium thiophenoxide  Δ  ->  o-,p- substituted diphenyl sulfide Secondary amine,  Δ  -> N -, o-,p- substi...

Significant figures   ( sig fig ),  aka  significant digits, are definite digits within a number written in positional notation that carry both reliability and requirement in conveying a specific quantity. If the number of figures exceeds what the instrument of measurement can resolve when presenting the outcome of a measurement ( viz. , mass, length, pressure, or volume), only the figures determined by the resolution are reliable; and therefore, considered significant. Question: What should be the reported value of the area of a wooden block having a length of 40.0 ± 0.5 mm and a breath of 20.0 ± 0.5 mm ? Solution: Click to enlarge the image Rules of  sig figs : # All non-zero numbers are significant. # Zeros between two non-zero digits are significant. # Leading zeros are NOT significant. # Trailing zeros to the right of the decimal are significant. # Trailing zeros in a whole number with the decimal shown are significant. # Trailing zeros in a whole number with n...

Resonance ( aka mesomerism ) is a way of describing bonding in certain molecules or ions by the combination of several contributing Lewis structures (or forms, aka resonance or canonical structures) that can be formed by delocalizing electrons of lone pairs ( lp ) or  π─bonds  into a resonance hybrid (or hybrid structure) in valence bond theory ( VBT ). The resonance hybrid, which is an average of the theoretical (or hypothetical) contributing structures, is an accurate representation for a molecule or an ion. Formic acid finds its uses in agriculture, energy, soldering, chromatography and as a reagent or a precursor in organic synthesis. Question: Arrange the following structures in the decreasing order of their stabilities: Click to enlarge the image Solution infographic: Click to enlarge the image Resonate with resonance❓ Let Chemaficionado know at mychemistryhomework@gmail.com ❗ References: (1)     Wikipedia Contributors.  Resonance (chemi...

Electromotive force ( EMF ) or electromotance is an energy transfer to an electric circuit per unit of electric charge. An electrochemical cell is a device that either generates electrical energy from chemical reactions in a so-called galvanic or voltaic cell, or induces chemical reactions (electrolysis) by applying external electrical energy in an electrolytic cell. The Nernst equation is a chemical thermodynamical relationship which allows the calculation of the reduction potential of a (half-cell/full-cell) reaction from the standard electrode potential, absolute temperature, the number of electrons involved in the redox reaction, and activities (often approximated by concentrations) of the chemical species undergoing reduction and oxidation respectively. Mnemonic: An Ox, Red Cat ( An ode Ox idation, Red uction Cat hode) Question: The EMF of a cell corresponding to the reaction Zn(s) + 2H + (aq) → Zn 2+ (0.1 M) + H 2 (g) (1 atm) is 0.28 V at 25 0 C . Calculate th...

An organic reaction in which an atom attached to an aromatic system (usually hydrogen) is substituted by an electrophile is referred to as  electrophilic aromatic substitution  ( S E Ar  or  EAS ). One of the most important  EASs  is bromination . Let's keep in mind that bromination may happen in a ring or in the side-chain depending on the reagent. Question: Predict the major product(s) of the following reaction: Click/tap to enlarge the image Solution infographic: Click/tap to enlarge the image If a strongly activating group competes with a weakly activating group in the same (or different) ring in the same compound, the strongly activating group wins for substitution despite steric effect. Eccentric EAS chemistry❓ Let Chemaficionado know  in the comments below or at mychemistryhomework@gmail.com ❗ References: (1)      Wikipedia Contributors.  Electrophilic aromatic substitution . Wikipedia. https://en.wikipedia.org/wiki/...

An organic reaction in which an atom attached to an aromatic system (usually hydrogen) is substituted by an electrophile is referred to as  electrophilic aromatic substitution  ( S E Ar  or  EAS ). One of the most important  EASs  is bromination . Let's recall that bromination may happen in a ring or in the side-chain depending on the reagent. Question: Predict the major product(s) of the following reaction: Click to enlarge the image Solution infographic: Click to enlarge the image If two deactivating groups compete with each other in the same (or different) ring in the same compound, the deactivating group with a  +M effect wins for substitution. A less sterically hindered position is preferred for substitution as well. What's elegant about the EAS chemistry❓ Let Chemaficionado know at mychemistryhomework@gmail.com ❗ References: (1)      Wikipedia Contributors.  Electrophilic aromatic substitution . Wikipedia. https://en.wikip...

Chemical equilibrium is the state in which both the reactants and products in a chemical reaction are present in concentrations that have no more propensity to change with time, s.t. there is no visible alteration in the system properties. This state results when the forward reaction proceeds at the same rate as the reverse/backward reaction, and is known as dynamic equilibrium. Vapor density is the density of a vapor in relation to that of hydrogen. Mnemonic :  ICE :  I nitial  C hange  E quilibrium (concentration or partial pressure) Question: The vapor density of a mixture consisting of NO 2 & N 2 O 4 is 38.3 at 2.67 0 C . Calculate the number of moles of NO 2 in 100 g of the mixture. Solution: Click/tap to enlarge the image α = Degree of dissociation, M = Molar mass, D = Vapor density Confused on vapor density vs. density❓ Let Chemaficionado know in the comments below or at mychemistryhomework@gmail.com ❗ References: (1)    ...