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Isomers are different compounds that have the same molecular formula ( MF ). When the group of atoms that form the molecules of different isomers are bonded together in fundamentally different ways, constitutional/structural isomers are formed. Question: How many isomeric bicycloalkanes do exist with the molecular formula C 8 H 14 ? Show their structures, IUPAC names and ring classes. Solution infographic: Click/tap to enlarge the image IHD = Index of hydrogen deficiency or degree of unsaturation ( DoU ) or ring plus double bond ( R+DB ) Irresistible isomers❓ Let Chemaficionado know in the comments below or at mychemistryhomework@gmail.com ❗ References: (1)       Structural isomer . Wikipedia. https://en.wikipedia.org/wiki/Structural_isomer. (2)      Wikipedia Contributors. IUPAC nomenclature of organic chemistry . Wikipedia. https://en.wikipedia.org/wiki/IUPAC_nomenclature_of_organic_chemistry.‌

The electron ( e − or β − in nuclear reactions) is a subatomic particle that has negative one elementary electric charge and negligible mass. The wave-particle duality of electrons has been established. Fun fact: Sir Joseph John Thomson, a British physicist, received the Nobel Prize in Physics “in recognition of the great merits of his theoretical and experimental investigations on the conduction of electricity by gases.” 31 years later, his son, Sir George Paget Thomson, a British experimental physicist, shared the Nobel Prize in Physics with Clinton Davisson “for their experimental discovery of the diffraction of electrons by crystals.” It is said the father won the Nobel for showing the electron is a particle, while the son for demonstrating it is a wave! Question: What is the ratio of frequency of revolution of an electron in the second excited state of He + to that in the second state of H ? Solution: Click/tap to enlarge the image ν = Frequency, u = Velocity, r ...

Enantiomeric excess ( ee ) is a purity quantification for chiral compounds in stereochemistry and reflects the degree to which a sample contains one enantiomer in greater amounts than the other. A racemic mixture has an ee of 0% , while a single completely pure enantiomer has an ee of 100% . So, for one, a sample with 70% of one enantiomer and 30% of the other has an ee of 40%. ee is used as one of the indicators of success of an asymmetric synthesis. ee is defined as the absolute difference between the mole fraction of each enantiomer. Click/tap to enlarge the image Question: Pure ( S )-Butan-2-ol has a specific rotation of +13.52 0 . A sample of Butan-2-ol prepared in the lab and purified by distillation has a calculated specific rotation of +6.76 0 . What can you conclude about the composition? Solution: Click/tap to enlarge the image N.B. 50% racemic Outstanding optical purity❓ Let Chemaficionado know in the comments below or at mychemistryhomework@gmail.com ❗ References:...

Stoichiometry is the relationship between the quantities of reactants and products before, during, and after chemical reactions. A chemical equation is the representation of a chemical reaction in the form of symbols and chemical formulas. The coefficients next to the symbols and formulas of entities are the absolute values of the stoichiometric numbers. Question: 0.6 g of a sample consisting of only CaC 2 O 4 & MgC 2 O 4 is heated at 500°C , gets converted into  CaCO 3 & MgCO 3 . The sample is then weighed 0.465 g . If the sample had been heated to 900°C where the products would be CaO & MgO , what would the mixture of oxides weigh? Solution: Click/tap to enlarge the image Sizzling stoichiometry❓ Let Chemaficionado know in the comments below or at mychemistryhomework@gmail.com ❗ References: (1)      Ncert. Chemistry : Textbook for Class XI - Part.I ; National Council Of Educational Research And Training: New Delhi. ‌(2)   ...

Enantiomeric excess ( ee ) is a purity quantification for chiral compounds in stereochemistry and reflects the degree to which a sample contains one enantiomer in greater amounts than the other. A racemic mixture has an ee of 0% , while a single completely pure enantiomer has an ee of 100% . So, for one, a sample with 70% of one enantiomer and 30% of the other has an ee of 40%. ee is used as one of the indicators of success of an asymmetric synthesis. ee is defined as the absolute difference between the mole fraction of each enantiomer. Click/tap to enlarge the image Question: Calculate the enantiomeric excess of the mixture containing 6 g of (+)-2-Butanol & 4 g of (─)-2-Butanol. Solution: Click/tap to enlarge the image Eerie enantiomeric excess❓ Let Chemaficionado know in the comments below or at mychemistryhomework@gmail.com ❗ References: (1)      Brown, C.; Ford, M. Higher Level Chemistry , 2nd ed.; Pearson Education: Harlow, Essex, 2014. (2)...

A reducing agent may or may not be selective in an organic reaction. The nature of reduction may change depending on the stoichiometric use and/or elevated temperature and/or use of another reagent like a catalyst. If the product has a new chiral center, stereoisomers may be obtained. Question: Predict the reagent(s) of the following reactions: Click/tap to enlarge the image Solution infographic: Click/tap to enlarge the image Diisobutylaluminum hydride ( DIBALH , DIBAL , DIBAL-H or DIBAH ) is an organometallic, selective reducing agent (chemoselectivity) that does not touch a C=C double bond or reduce a CN to CH 2 OH . Reckless reducing agents❓ Let Chemaficionado know in the comments below or at mychemistryhomework@gmail.com ❗ References: (1)      Wikipedia Contributors. Diisobutylaluminium hydride . Wikipedia. (2)      Brown, C.; Ford, M. Higher Level Chemistry , 2nd ed.; Pearson Education: Harlow, Essex, 2014. (3)      Ncert. Chemi...

Close-packing of spheres in geometry is a dense, infinite, regular arrangement of congruent, identical spheres in an arrangement ( aka lattice). 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 face-centered cubic ( cF or fcc ). Question: What is the total atom number in a diamond unit cell ( fcc type with  4 unshared tetrahedrally bonded atoms )? Solution: Click/tap to enlarge the image Solid understanding of solid state❓ Let Chemaficionado know in the comments below or 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...

Colligative properties are those properties of solutions which depend on the ratio of the number of solute particles to that of solvent particles in a solution, and not on the nature of the chemical species present. The van 't Hoff factor i is a measure of the effect of a solute on colligative properties, viz. , relative lowering in vapor pressure, boiling-point elevation, freezing-point depression and osmotic pressure, and is the ratio of the actual (experimental/observed) concentration of particles produced when the substance is dissolved to the formal (theoretical/normal) concentration that would be expected from its chemical formula. For most non-electrolytes dissolved in water, the factor is basically 1 . Question: K 4 [Fe(CN) 6 ] is supposed to be 40% dissociated when 1 M solution is prepared. Its boiling point is equal to that of another solution of 20% w/v of A (non-electrolyte). Considering Molality m = Molarity M , what the molecular weight of A ? Solutio...

A reaction rate constant/coefficient k is a proportionality constant which quantifies the rate and direction of a chemical reaction by relating it with the concentration of reactants in chemical kinetics. The order of reaction is a number which quantifies the degree to which the rate of a chemical reaction depends on concentrations of the reactants. In other words, the order of reaction is the exponent to which the concentration of a particular reactant is raised. For instance, the rate law can be expressed as: Rate = k [A] x [B] y where k = Rate constant, A & B are reactants and x & y are the orders of the reaction w.r.t. A & B respectively. Mnemonic: The absolute value of the exponents of L & mol one less than the reaction order Question: What is the unit of the rate constant for a reaction that occurs between two second-order reactants? Solution: Click/tap to enlarge the image For 2 nd order, L 1 mol ─1 s ─1 or M ─1 s −1 For 1 st ...

The Planck relation ( aka Planck's energy–frequency relation , the Planck–Einstein relation , or Planck equation ) is a fundamental equation in quantum mechanics which states that the energy difference ΔE  in an atomic electron transition is proportional to the photon frequency ν, i.e., ΔE = hν ( h = Planck constant ). The photon velocity c is related to ν & photon wavelength λ as c = ν λ . ΔE of an electron during a transition from the initial state n i to the final state n f in an H- like atom is expressed as: ΔE = 2.18 x 10 ─18 Z 2 (1/n i 2 ─ 1/n f 2 ) J/ electron ( Z = Atomic number) Question: What is the wavelength of a photon emitted during a transition from n = 5 state to the n = 2 state in the H atom? Solution: Click/tap to enlarge the image This transition gives rise to a spectral line in the visible region of the Balmer series . Exciting electron transition❓ Let Chemaficionado know in the comments below or at mychemistryhomework@gmai...

The Beer–Lambert law ( aka Beer's law ) can be used to determine the concentration of substances in a solution and describes how the amount of light that a solution absorbs is directly proportional to the solution's concentration. The equation is: A = ε c l where A = Absorbance, ε = Absorption coefficient ( aka molar absorptivity), c = Concentration of the absorbing substance in mol/L , l = Path length in cm The law is valid only under certain conditions. If an absorbance A versus time t plot is made, the rate of disappearance of a substance can be calculated from the slope at a certain time and the molar absorptivity. The order of reaction is a number which quantifies the degree to which the rate of a chemical reaction depends on concentrations of the reactants. In other words, the order of reaction is the exponent to which the concentration of a particular reactant is raised. For instance, the rate law can be expressed as: Rate = k [A] x [B] y where k = Rate consta...

The energy required to remove an electron ( e ─ ) from the isolated atom/ion in the gaseous state of an element to form a cation is referred to as the ionization energy/enthalpy/potential (IE/IP) . For an element,  IE  involves an endothermic reaction; and in general, IE 3 > IE 2 > IE 1 . The energy released to add an e ─ to the isolated atom/ion in the gaseous state of an element to form an anion is known as the electron affinity ( EA ) or electron gain enthalpy. For an element,  EA  involves an exothermic reaction. Question: The first ( Δ i H 1 ) and the second ( Δ i H 2 ) ionization enthalpies (in kJ mol –1 ) and the ( Δ eg H ) electron gain enthalpy (in kJ mol –1 ) of a few elements are given below: Element Δ i H 1 Δ i H 2 Δ eg H I 520 7300 ─60 II 419 3051 ─48 III 1681 3374 ─328 ...