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Isomers are different compounds that have the same molecular formula. When the group of atoms that form the molecules of different isomers are bonded together in fundamentally different ways, constitutional/structural isomers are formed. Isomers that differ only in the spatial orientation/configuration of their component atoms are referred to as stereoisomers or spatial isomers. Question: How many isomers (including stereoisomers) do exist with the molecular formula C 4 H 8 ? Solution infographic: Click/tap to enlarge the image MF = Molecular formula, DBE = Double bond equivalent, DU = Degree of unsaturation, IHD = Index of hydrogen deficiency Tip for drawing the parent hydrocarbon chain:  The beginners are encouraged to use the condensed structural formulae for a better understanding. # Draw the C -atoms of the parent chain right to left keeping enough space between the atoms so that the bonds and the H -atoms with their indices may be inserted later. # Draw single bonds bet...

A  stereocenter   (or stereogenic center) of a molecule is an atom (center), axis or plane, which is the focus of spatial isomerism (or stereoisomerism). When having at least three different groups bound to the stereocenter, interchanging any two different groups creates a new stereoisomer ( SI ). Question: Predict the possible stereoisomers of the follow molecule: H 3 C─CH=CH─CH=CH─CH=CH─CH 3 Solution infographic: Click/tap to enlarge the image Like 3D chemistry❓ Let Chemaficionado know  in the comments below or at mychemistryhomework@gmail.com ❗ References: (1)      Stereocenter . Wikipedia. https://en.wikipedia.org/wiki/Stereocenter. (2)      Chouhan, M. S.  Advanced Problems in Organic Chemistry for JEE , 11th Ed. (3)      Wikipedia Contributors.  Cis–trans isomerism . Wikipedia. https://en.wikipedia.org/wiki/Cis%E2%80%93trans_isomerism.

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 halogenation. If Bromine water is added to Aniline, a multi-substituted product ( 2,4,6 -derivative) is obtained as Aniline is a strongly activating group (the same happens to Phenol). To generate the mono-substituted product, a protection, say, an acyl group is required. Question: Predict the major product(s) of the following reaction: Click/tap to enlarge the image Solution infographic: Click/tap to enlarge the image Motivated by EAS ❓ 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/Electrophilic_aromatic_substitution. (2)    ...

In thermodynamics the reference is the internal energy (in chemistry). The internal energy of a thermodynamic system is the energy of the system as a state function, measured as the amount of energy required to bring the system from its standard internal state to its internal state of interest. The enthalpy of fusion ( aka the (latent) heat of fusion) is the amount of energy (enthalpy/heat) that must be added to a solid substance to transform a quantity of that substance into a liquid, and a function of the pressure and temperature at which the transformation occurs. Latent heat ( aka latent energy or heat of transformation) is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process. Question: Assuming the water vapor to be a perfect gas, calculate the internal energy change when 1 mol of water at 100°C and 1 bar pressure is converted to ice at 0°C . Given standard  ΔH fus   of ice = 6.00 kJ mol -1 and the heat c...

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. The equilibrium constant of a chemical reaction is the value of its reaction quotient at chemical equilibrium. For a given set of reaction conditions like temperature, solvent, and ionic strength, the equilibrium constant is independent of the initial concentrations of the reactants and products. The equilibrium constant will be dimensionless only if the number of moles of the reactants is equal to that of the products. Let’s recall that the partial pressures of the gases in a mixture tell us the relative number of particles or moles of the gases in that mixture. The Gibbs free energy (or Gibb...

The Grignard reagent is synthetically versatile as the organomagnesium compound can react with a variety of electrophiles . The mechanism is not well-understood and most likely involves a single electron transfer ( SET ). The substrate must not have any acidic groups. The reactions require dry solvents such as THF ( Tetrahydrofuran ). Question: Predict the major product(s) of the following reaction: Click/tap to enlarge the image Solution infographic: Click/tap to enlarge the image Gazed at the Grignard reactions❓ How about a whopping wheel (click HERE ) ❓ Let Chemaficionado know  in the comments below or at mychemistryhomework@gmail.com ❗ References: (1)      Grignard reagent . Wikipedia. https://en.wikipedia.org/wiki/Grignard_reagent. ‌(2)      Grignard reaction . Wikipedia. https://en.wikipedia.org/wiki/Grignard_reaction.

Multistep synthesis is the artificial execution of multiple organic chemical reactions to obtain one or more products by physical and chemical manipulations. Retrosynthetic analysis is a problem-solving approach in the organic syntheses, achieved by transforming a target molecule into simpler precursor structures regardless of any potential reactivity/interaction with reagents, and repeated until a simple or commercially available structure is reached, which can be used as a starting material to synthesize the target molecule. Glycerol finds its applications in food/medical/ entertainment industry , botanical extracts, electronic cigarette liquid,  vibration damping, or  as an antifreeze/ ultrasonic couplant/ internal combustion fuel ,  or a chemical intermediate. Question: How would you do the following transformation? Click/tap here to enlarge the image Solution infographic: Click/tap here to enlarge the image A E = Electrophilic addition, S N 2 = Nucleophilic su...

The cubic (or isometric) crystal system in crystallography is a crystal system where the unit cell is in the shape of a cube, one of the most common and simplest shapes found in crystals and minerals. One of the three main varieties of these crystals is body-centered cubic ( cI  or bcc ). Question: An element has a bcc structure with a cell edge of 288 pm . The density of the element is 7.2 g/cm 3 . How many atoms are present in 208 g of the element? Solution: Click to enlarge the image m = Mass, r = Density, Z = Net lattice points Does solid state make you contemplate❓ Let Chemaficionado know at mychemistryhomework@gmail.com ❗ References: (1)      Wikipedia Contributors.  Cubic crystal system . Wikipedia. https://en.wikipedia.org/wiki/Cubic_crystal_system. ‌(2)     Ncert.  Chemistry : Textbook for Class XI - Part.I ; National Council Of Educational Research And Training: New Delhi.

The enthalpy of combustion of a substance, usually a fuel/food, is the amount of enthalpy/heat/energy released (in calorie/Joule) during the combustion/burning of a given amount of it. The enthalpy of combustion always has a negative value (exothermic reaction). Question: 2CH 6 N 2 (l) + 5O 2 (g) → 2N 2 (g) + 2CO 2 (g) + 6H 2 O(g) The combustion of Methylhydrazine, a common rocket fuel, is represented above. ΔH r = –1303 kJ mol −1 . What would be the ΔH per mol of CH 6 N 2 (l) if the reaction produced H 2 O(l) instead of H 2 O(g)? ( ΔH for the condensation of H 2 O(g) to H 2 O(l) = –44 kJ mol −1 ) Solution: Click to enlarge the image Is it challenging to recall that the enthalpy of reaction is per mole❓ Let Chemaficionado know at mychemistryhomework@gmail.com ❗ References: (1)      Wikipedia Contributors.  Heat of combustion . Wikipedia. https://en.wikipedia.org/wiki/Heat_of_combustion. ‌(2)     Ncert.  Chemistry : Textbook fo...

The  standard molar entropy  is referred to as the entropy content of one mole of a pure substance (typically) at the standard temperature and pressure. Let’s recall that the second law of thermodynamics establishes the concept of entropy as a physical property of a thermodynamic system. For a molecule, entropy may be translational, rotational and vibrational. Question: Arrange the following in the increasing order of the standard molar entropies  (S Ѳ ): CH 3 Cl(g), CH 2 Cl 2 (g) and CHCl 3 (g) Solution: Click to enlarge the image Entropy explained or it's still a disorder ❓ Let Chemaficionado know at mychemistryhomework@gmail.com ❗ References: (1)      Wikipedia Contributors.  Moment of inertia . Wikipedia. https://en.wikipedia.org/wiki/Moment_of_inertia. (2)      Wikipedia Contributors.  Second law of thermodynamics . Wikipedia. https://en.wikipedia.org/wiki/Second_law_of_thermodynamics. (3)      Wikipedia Contri...

Removal of two substituents from a molecule in either a one- or two-step mechanism is referred to as  elimination reaction  in organic chemistry. The  β -elimination is the most popular. An elimination reaction may involve regiochemistry and/or stereochemistry. Zaytsev's rule ( aka Zaitsev's/Saytzeff's/Saytzev's rule) is an empirical rule for predicting the favored alkene product(s) in elimination reactions (removal of H from the α-C having the fewest H -substituents, which means most substituted alkene => most stable; Mnemonic : Poor becomes poorer). However, exceptions exist, i.e. , removal of H from the α-C having the most H -substituents takes place to give a Hofmann product. Question: Predict the major product(s) of the following reaction: Click/tap to enlarge the image Solution infographic: Click/tap to enlarge the image E2 = Elimination bimolecular Want more on elimination reactions ❓Click HERE for a wheel❗ Questions ❓ Let Chemaficionado know  in t...

There exist three definitions in common use of the word ‘ base ’: Arrhenius bases , Brønsted bases , and Lewis bases . In the current scenario, we will be using a Lewis base, which is any species that has a filled orbital containing an electron pair which is not involved in bonding but may form a coordinate/dative bond with a Lewis acid to form a Lewis adduct or may accept a proton. Resonance or delocalization of electrons typically reduces the basicity of the N -atom in an organic compound since basicity means an ability to donate an electron pair according to Lewis. Caffeine is a CNS (central nervous system) stimulant of the methylxanthine class, and is the most consumed psychoactive substance globally used for its eugeroic (promoting wakefulness), ergogenic (enhancing physical performance), or nootropic (enhancing cognition) properties, and for recreational purpose or in social settings in the form of coffee, tea, soft drink, energy drink and so on. Question: Arrange the N -atoms o...

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. The equilibrium constant of a chemical reaction is the value of its reaction quotient at chemical equilibrium. For a given set of reaction conditions like temperature, solvent, and ionic strength, the equilibrium constant is independent of the initial concentrations of the reactants and products. The equilibrium constant will be dimensionless only if the number of moles of the reactants is equal to that of the products. Let’s recall that the partial pressures of the gases in a mixture tell us the relative number of particles or moles of the gases in that mixture. Mnemonic : ICE : I nitial C hange E qu...

Vapor pressure  or equilibrium vapor pressure, an indication of a liquid's thermodynamic tendency to evaporate, is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid/liquid) at a given temperature in a closed system. Raoult's law states that the partial pressure of each component of an ideal mixture of liquids is equal to the vapor pressure of the pure component (liquid/solid) multiplied by its mole fraction in the mixture. Dalton's law ( aka Dalton's law of partial pressures) states that the total pressure exerted is equal to the sum of the partial pressures of the individual gases in a mixture of non-reacting ideal gases. Question: The vapor pressure of EtOH & MeOH are 44.5 & 88.7 mm Hg respectively. An ideal solution is formed at the same temperature by mixing 60 g of EtOH with 40 g of MeOH. Calculate the mole fraction of MeOH in the vapor. Solution: Click to enlarge the image Χ  = Mole fraction, MW = Mol...