BCHET-147 Solved Assignment January 2026 | ORGANOMETALLICS, BIOINORGANIC CHEMISTRY, POLYNUCLEAR HYDROCARBONS AND UV, IR SPECTROSCOPY | IGNOU BSCG

Q1. What is the chromyl chloride test? Give suitable equations.

Key Points:

Chromyl chloride test qualitatively detects chloride ions (Cl⁻) in salts.
It involves heating a chloride salt with K₂Cr₂O₇ and concentrated H₂SO₄.
A volatile, red-orange chromyl chloride (CrO₂Cl₂) vapor is formed.
CrO₂Cl₂ vapor reacts with NaOH to produce a yellow sodium chromate solution.

Answer: The chromyl chloride test is a qualitative chemical test used for the detection of chloride ions (Cl⁻) in inorganic salts. This test is highly specific for chlorides, as bromides and iodides do not yield similar volatile compounds under the same conditions. To perform the test, a small amount of the solid chloride salt is mixed with solid potassium dichromate (K₂Cr₂O₇) and concentrated sulfuric acid (H₂SO₄). Upon gentle heating, a volatile, dark red-orange vapor of chromyl chloride (CrO₂Cl₂) is...

Q2. Give the structure of dimethyl beryllium.

Key Points:

Dimethyl beryllium, (CH₃)₂Be, forms a polymeric structure in the solid state.
Each beryllium atom is tetrahedrally coordinated to four methyl groups.
Methyl groups act as bridging ligands between two beryllium atoms, forming an infinite chain.
The bonding in the bridges involves 3-center-2-electron (electron-deficient) bonds.

Answer: Dimethyl beryllium, (CH₃)₂Be, exhibits a unique polymeric structure in its solid state due to the electron-deficient nature of beryllium. In this polymeric arrangement, each beryllium atom is tetrahedrally coordinated. It forms bonds with four methyl groups, but not in a simple four-coordinate fashion like carbon. Instead, two methyl groups are terminal, and two methyl groups act as bridging ligands between two beryllium atoms. The bridging methyl groups are characteristic of electron-deficien...

Q3. Explain the concept of hapticity with reference to allyl complexes, such as [Pd(η³-C3H5)Cl]. How does η³-coordination differ from η¹-coordination in terms of bonding and structure?

Key Points:

Hapticity (η) indicates the number of contiguous ligand atoms simultaneously bonded to a metal centre.
η³-coordination in allyl complexes means all three carbon atoms are simultaneously bonded via delocalized π-electrons.
[Pd(η³-C₃H₅)Cl] exemplifies η³-allyl, where the ligand is multihapto with equal C-C bond lengths.
η¹-coordination involves only one carbon atom forming a localized σ-bond with the metal.

Answer: Hapticity, denoted by the Greek letter η (eta), describes the number of contiguous atoms in a ligand that are simultaneously bonded to a central metal atom. For instance, in an allyl complex like [Pd(η³-C₃H₅)Cl], the η³ notation signifies that all three carbon atoms of the allyl ligand are directly coordinated to the palladium metal. In η³-coordination, the allyl ligand (C₃H₅) acts as a delocalized π-system. It is typically considered an allyl anion (C₃H₅⁻) contributing four electrons or an all...

Q4. Explain the structure of Fe2(CO)9 based on valence bond approach.

Key Points:

Fe₂(CO)₉ is a dinuclear iron carbonyl complex featuring an Fe-Fe single bond.
It contains six terminal CO ligands (three per Fe) and three bridging CO ligands.
The three bridging COs symmetrically connect the two iron centers, forming a shared face.
Each iron atom in Fe₂(CO)₉ satisfies the 18-electron rule for stability.

Answer: Fe₂(CO)₉ is a classic dinuclear organometallic compound, whose structure is effectively explained using the valence bond approach. This complex features two iron atoms directly bonded to each other, forming a stable Fe-Fe single bond. In its structure, six carbonyl (CO) ligands are terminal, with three bonded to each iron atom in an essentially fac-arrangement. The remaining three CO ligands act as bridging ligands, symmetrically connecting the two iron centers. These bridging carbonyls, along ...

Q5. How can formation of nitrosyl complexes be formed from carbonyl complexes with the help of nitric oxide? Give three suitable equations to show this.

Key Points:

Nitric oxide (NO) is a versatile ligand, replacing carbonyls (CO) in metal complexes.
NO often acts as a 3-electron donor (NO⁺) in these substitution reactions.
CO is a 2-electron donor; its replacement by NO adjusts the electron count for stability.
Fe(CO)₅ reacts with 2NO to form Fe(CO)₂(NO)₂, releasing 3CO ligands.

Answer: Nitrosyl complexes can be formed from carbonyl complexes through ligand substitution reactions involving nitric oxide (NO). Nitric oxide is a highly versatile ligand, capable of replacing carbonyl (CO) ligands, often acting as a three-electron donor (NO⁺) while CO is a two-electron donor. This substitution often leads to the formation of stable complexes that typically adhere to the 18-electron rule, sometimes accompanied by changes in the formal oxidation state of the metal or the expulsion of ...

Q6. The C – O stretching frequencies in the IR spectra of certain metal carbonyl species are as follows:Ni(CO)4 2056 cm-1[Fe(CO)6]2+ 2200cm-1The value for CO(g) is 2143 cm¯¹. Discuss

Key Points:

C–O stretching frequency indicates C–O bond strength in IR spectra.
Ni(CO)4 shows lower ν(CO) (2056 cm⁻¹) due to strong pi-backbonding from electron-rich Ni(0).
Pi-backbonding weakens C–O bond, lowering its vibrational frequency.
[Fe(CO)6]2+ shows higher ν(CO) (2200 cm⁻¹) due to weak pi-backbonding from electron-poor Fe(II).

Answer: The C–O stretching frequency in IR spectroscopy is a crucial indicator of the C–O bond strength, which is significantly influenced by the nature of bonding in metal carbonyls, as discussed in the BCHET-147 course material. For free carbon monoxide, CO(g), the C–O stretching frequency is 2143 cm⁻¹, corresponding to a strong triple bond. In Ni(CO)4, the C–O stretching frequency is observed at 2056 cm⁻¹, which is lower than that of free CO. This reduction is attributed to strong synergistic bondi...

Q7. What information is obtained from the IR spectrum of Fe2(Cp)2(CO)4 given below ?

Key Points:

IR spectrum identifies CO bonding modes (terminal vs. bridging).
Terminal CO stretches occur at higher frequencies (1900-2150 cm⁻¹).
Bridging CO stretches occur at lower frequencies (1750-1850 cm⁻¹).
Fe₂(Cp)₂(CO)₄ IR shows distinct bands for both terminal and bridging COs.

Answer: The Infrared (IR) spectrum of organometallic compounds, particularly metal carbonyls like Fe₂(Cp)₂(CO)₄, provides crucial information about the nature and bonding modes of the carbonyl ligands. It is a highly sensitive tool to distinguish between terminal and bridging carbonyl groups based on their characteristic stretching frequencies (νCO). Terminal carbonyls (M-C≡O) generally exhibit stretching frequencies in the higher region, typically between 1900-2150 cm⁻¹. This is due to the greater bon...

Q8. Which metal ion is essential for the process of blood coagulation? Explain the mechanism by which it facilitates clot formation? Give the different ways by which cadmium affects the human body.

Key Points:

Calcium ion (Ca²⁺) is essential for blood coagulation.
Ca²⁺ acts as a cofactor for vitamin K-dependent clotting factors.
Ca²⁺ enables clotting factors to bind to platelet surfaces for activation.
It is crucial for prothrombin to thrombin conversion and fibrin formation.

Answer: Calcium ion (Ca²⁺) is the essential metal ion for the process of blood coagulation. This divalent cation plays a pivotal role by acting as a crucial cofactor for several enzymes and proteins involved in the coagulation cascade, facilitating the rapid formation of a stable blood clot. In the mechanism of clot formation, Ca²⁺ ions are vital for the activation of vitamin K-dependent clotting factors, such as factors II (prothrombin), VII, IX, and X. These factors possess γ-carboxyglutamate residue...

Q9. With the help of a suitable diagram explain the Na⁺-K⁺ pump. Show how the sodium-potassium pump moves toward an equilibrium state with the relative concentrations.

Key Points:

Na⁺-K⁺ pump is an active transport ATPase, requiring ATP.
It pumps 3 Na⁺ ions out of the cell and 2 K⁺ ions into the cell.
ATP hydrolysis drives conformational changes for ion translocation.
The pump creates and maintains steep Na⁺ and K⁺ electrochemical gradients.

Answer: The Na⁺-K⁺ pump, also known as the Na⁺/K⁺-ATPase, is a vital integral membrane protein responsible for active transport in animal cells. It utilizes the energy derived from ATP hydrolysis to transport sodium (Na⁺) ions out of the cell and potassium (K⁺) ions into the cell, against their respective concentration gradients. A suitable diagram (imagined as a multi-step cycle) would illustrate the pump's conformational changes. Initially, the pump, open to the intracellular side, binds three Na⁺ io...

Q10. With the help of a suitable diagram, explain the mechanism of oxygen binding in hemoglobin and discuss the structural changes that occur upon formation of oxyhemoglobin.

Key Points:

Deoxyhemoglobin Fe²⁺ is high-spin, out of porphyrin plane, linked to proximal His F8 (T-state).
Oxygen binding to Fe²⁺ causes spin state change, pulling Fe²⁺ into the porphyrin plane.
Fe²⁺ movement pulls proximal His F8 and attached F-helix, initiating structural changes.
Inter-subunit salt bridges and H-bonds stabilizing the T-state break upon O₂ binding.

Answer: Hemoglobin, a tetrameric protein, utilizes four heme groups for cooperative oxygen binding. In deoxyhemoglobin (the T-state), the central ferrous iron (Fe²⁺) in each heme is high-spin and pentacoordinated, covalently linked to a proximal histidine (His F8). Due to its larger ionic radius, this high-spin Fe²⁺ atom is slightly displaced approximately 0.4 Å out of the porphyrin plane, giving the heme a 'puckered' conformation. Upon oxygen binding, O₂ acts as the sixth ligand to the Fe²⁺, forming o...

Q11. How will you prepare 5-hexen-2-one from ethyl 3-oxobutanoate. Give the reactions involved and the reagents used in the reaction.

Key Points:

Acetoacetic ester synthesis uses ethyl acetoacetate to form substituted methyl ketones.
Sodium ethoxide deprotonates ethyl acetoacetate to create a nucleophilic enolate.
The enolate attacks 1-bromo-3-butene via S_N2 alkylation to form an intermediate.
Acidic hydrolysis converts the alkylated ester into a β-keto acid.

Answer: To synthesize 5-hexen-2-one from ethyl 3-oxobutanoate (ethyl acetoacetate), a modified acetoacetic ester synthesis is employed. This fundamental method, covered in BCHET-147, Unit 13 (Reactions of β-Dicarbonyl Compounds), is excellent for preparing substituted methyl ketones. First, ethyl 3-oxobutanoate is treated with a strong base, typically sodium ethoxide (NaOEt) in ethanol. This deprotonates the highly acidic α-hydrogen of the active methylene group, forming a resonance-stabilized enolate ...

Q12. Give IUPAC names of the following compounds. Is napthalene an aromatic compound? Explain.

(a)) Give IUPAC names of the following compounds. (80 words)
(b)) Is napthalene an aromatic compound? Explain. (120 words)

Key Points:

IUPAC naming involves identifying the parent chain/ring and numbering substituents for lowest locants.
Aromatic compounds must be cyclic, planar, fully conjugated, and contain (4n+2) π electrons.
Hückel's rule (4n+2 π electrons) is a primary criterion for aromaticity.
Naphthalene is a bicyclic, planar, fully conjugated molecule with 10 π electrons.

Answer:

Q13. Give the reaction involved and the reagents used for the commercial preparation of pyrrole.

Key Points:

Commercial pyrrole is prepared from furan and ammonia.
The reaction is a catalytic vapor-phase process.
Aluminum oxide (Al₂O₃) or silica-alumina is the common catalyst.
High temperatures (400-500 °C) are required for the reaction.

Answer: The commercial preparation of pyrrole predominantly involves a catalytic vapor-phase reaction between furan and ammonia. This method is highly favored in industry due to the economic viability and widespread availability of the starting materials, ensuring cost-effective large-scale production of this vital heterocyclic compound. The primary reagents employed in this commercial synthesis are furan, a five-membered heterocyclic ether, and ammonia (NH₃). Furan can be readily obtained from furfura...

Q14. Give the resonance structures for the intermediate in the reaction where electrophile E+ attacks on 2-position of pyridine.

Key Points:

Electrophilic attack at pyridine's 2-position forms a sigma complex intermediate.
First resonance structure: E at C-2, positive charge at C-3.
Second resonance structure: E at C-2, positive charge delocalized to C-5.
Third resonance structure: E at C-2, positive charge on the nitrogen atom.

Answer: When an electrophile (E⁺) attacks the 2-position of pyridine, a sigma complex, also known as a Wheland intermediate, is formed. This intermediate is a carbocation which is stabilized by resonance, allowing the positive charge to be delocalized across several atoms in the ring. Upon attack at C-2, the pi electrons of the C2-C3 bond form a new bond with the electrophile at C-2. This initial step leaves a positive charge on the adjacent carbon atom, C-3. This structure, with E attached to C-2 and ...

Q15. What are the differences between Bathochromic shift and Hypsochromic shift?

Key Points:

Bathochromic shift (red shift): absorption band moves to longer wavelength (λmax), lower energy.
Hypsochromic shift (blue shift): absorption band moves to shorter wavelength (λmax), higher energy.
Bathochromic shift is caused by increased conjugation or presence of auxochromes.
Hypsochromic shift results from decreased conjugation or protonation of auxochromes.

Answer: In UV-Vis spectroscopy, as discussed in the BCHET-147 course materials under the UV-IR Spectroscopy unit, two significant shifts in absorption maxima are the Bathochromic and Hypsochromic shifts. A **Bathochromic shift**, commonly known as a "red shift," describes the movement of an absorption band to a longer wavelength (λmax) and consequently lower energy. This shift often occurs due to an increase in the extent of conjugation within a chromophore, such as adding more double bonds, or the int...

Q16. Explain Woodward rules for predicting π-π* absorption in dienes.

Key Points:

Woodward-Fieser rules predict λmax for π-π* electronic transitions in conjugated dienes.
π-π* absorption involves exciting a π electron from HOMO to LUMO antibonding π* orbital.
Base value for heteroannular (or acyclic) diene is 214 nm.
Base value for homoannular diene (double bonds in same ring) is 253 nm.

Answer: The Woodward-Fieser rules are empirical guidelines used to predict the wavelength of maximum absorption (λmax) for π-π* electronic transitions in conjugated dienes in the ultraviolet-visible (UV-Vis) region. These rules are fundamental for correlating molecular structure with UV absorption properties, particularly aiding in the structural elucidation of organic compounds. π-π* absorption occurs when a conjugated system absorbs UV radiation, causing an electron to be promoted from a bonding π mo...

Q17. What sort of shift may be observed in bromobenzene, (C6H5Br)?

Key Points:

Bromine's electronegativity causes inductive electron withdrawal in bromobenzene.
Inductive withdrawal leads to deshielding, shifting aromatic NMR signals *downfield* (higher δ).
Aromatic protons in bromobenzene exhibit distinct deshielded signals in ¹H NMR.
Ortho protons are typically the most deshielded due to proximity to the bromine atom.

Answer: In bromobenzene (C₆H₅Br), the presence of the bromine atom, an electronegative substituent, significantly alters the electronic environment of the benzene ring, leading to distinct chemical shifts in its Nuclear Magnetic Resonance (NMR) spectra. For the aromatic protons (¹H NMR), bromine exerts an inductive electron-withdrawing effect. This withdrawal of electron density deshields the nearby protons, causing their NMR signals to shift *downfield* (towards higher δ values) compared to the shield...

Q18. Explain the Feiser and Scott rules for predicting π- π* absorption in α, β-unsaturated ketones (enones) and aldehydes.

Key Points:

Fieser and Scott rules predict λmax for π-π* absorption in α,β-unsaturated ketones and aldehydes.
The method uses an additive approach: base value plus specific increments for substituents.
Base values: 215 nm (6-ring/acyclic enone), 202 nm (5-ring enone), 210 nm (enal).
Alkyl/ring residue increments: α (+10 nm), β (+12 nm), γ/δ (+18 nm).

Answer: The Fieser and Scott rules, also known as Woodward-Fieser rules, are an empirical set of guidelines used to predict the wavelength of maximum π-π* absorption (λmax) for α,β-unsaturated ketones (enones) and aldehydes (enals) in the ultraviolet-visible (UV-Vis) spectrum. These rules are vital for structural determination and understanding the electronic transitions within conjugated systems. This methodology involves starting with a specific base value, which is dependent on the fundamental chrom...

Q19. With the help of suitable diagrams explain how the IR spectrum is depicted in the absorption mode and the transmittance mode.

Key Points:

IR spectroscopy measures molecular vibrations through IR radiation absorption.
Absorption mode plots Absorbance (A) vs. Wavenumber (cm⁻¹), with peaks pointing upwards.
Transmittance mode plots Percent Transmittance (%T) vs. Wavenumber (cm⁻¹), showing downward troughs.
Higher absorbance in absorption mode corresponds to lower %T in transmittance mode.

Answer: Infrared (IR) spectroscopy investigates molecular vibrations by measuring the absorption of IR radiation, providing characteristic spectra for compound identification and functional group analysis. The representation of this spectrum can be done in two main modes: absorption and transmittance. In the absorption mode, the IR spectrum is depicted by plotting Absorbance (A) on the y-axis against wavenumber (cm⁻¹) on the x-axis. In this representation, peaks rise upwards from the baseline, with the...

Q20. The IR spectrum of a sample of cyclohexanol is recorded. Which major absorption bands you would be looking for in the spectrum?

Key Points:

Cyclohexanol IR spectrum features primarily hydroxyl (-OH) and cyclohexyl C-H bonds.
Major O-H stretching vibration appears as a strong, broad band at 3600-3200 cm⁻¹ due to hydrogen bonding.
C-H stretching vibrations (sp³) from the cyclohexyl ring are seen at 3000-2850 cm⁻¹.
Characteristic C-O stretching vibration for alcohols is a strong band at 1260-1000 cm⁻¹.

Answer: Cyclohexanol is an alcohol, and its IR spectrum will exhibit several characteristic absorption bands primarily associated with the hydroxyl (-OH) group and the cyclohexyl ring's C-H bonds. The most prominent feature indicating the presence of an alcohol is the O-H stretching vibration. This band typically appears as a strong, broad absorption in the region of 3600-3200 cm⁻¹. Its broadness is a hallmark of hydrogen bonding between alcohol molecules. Secondly, the C-H stretching vibrations from t...

BCHET-147 Solved Assignment — January 2026 / July 2026

ORGANOMETALLICS, BIOINORGANIC CHEMISTRY, POLYNUCLEAR HYDROCARBONS AND UV, IR SPECTROSCOPY | IGNOU Bachelor of Science (General) (CBCS) (BSCG)

BCHET-147—January 2026 / July 2026

ORGANOMETALLICS, BIOINORGANIC CHEMISTRY, POLYNUCLEAR HYDROCARBONS AND UV, IR SPECTROSCOPY

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BCHET-147 Assignment Questions — January 2026

Q1. What is the chromyl chloride test? Give suitable equations.

Q2. Give the structure of dimethyl beryllium.

Q3. Explain the concept of hapticity with reference to allyl complexes, such as [Pd(η³-C3H5)Cl]. How does η³-coordination differ from η¹-coordination in terms of bonding and structure?

Q4. Explain the structure of Fe2(CO)9 based on valence bond approach.

Q5. How can formation of nitrosyl complexes be formed from carbonyl complexes with the help of nitric oxide? Give three suitable equations to show this.

Q6. The C – O stretching frequencies in the IR spectra of certain metal carbonyl species are as follows:Ni(CO)4 2056 cm-1[Fe(CO)6]2+ 2200cm-1The value for CO(g) is 2143 cm¯¹. Discuss

Q7. What information is obtained from the IR spectrum of Fe2(Cp)2(CO)4 given below ?

Q8. Which metal ion is essential for the process of blood coagulation? Explain the mechanism by which it facilitates clot formation? Give the different ways by which cadmium affects the human body.

Q9. With the help of a suitable diagram explain the Na⁺-K⁺ pump. Show how the sodium-potassium pump moves toward an equilibrium state with the relative concentrations.

Q10. With the help of a suitable diagram, explain the mechanism of oxygen binding in hemoglobin and discuss the structural changes that occur upon formation of oxyhemoglobin.

Q11. How will you prepare 5-hexen-2-one from ethyl 3-oxobutanoate. Give the reactions involved and the reagents used in the reaction.

Q12. Give IUPAC names of the following compounds. Is napthalene an aromatic compound? Explain.

Q13. Give the reaction involved and the reagents used for the commercial preparation of pyrrole.

Q14. Give the resonance structures for the intermediate in the reaction where electrophile E+ attacks on 2-position of pyridine.

Q15. What are the differences between Bathochromic shift and Hypsochromic shift?

Q16. Explain Woodward rules for predicting π-π* absorption in dienes.

Q17. What sort of shift may be observed in bromobenzene, (C6H5Br)?

Q18. Explain the Feiser and Scott rules for predicting π- π* absorption in α, β-unsaturated ketones (enones) and aldehydes.

Q19. With the help of suitable diagrams explain how the IR spectrum is depicted in the absorption mode and the transmittance mode.

Q20. The IR spectrum of a sample of cyclohexanol is recorded. Which major absorption bands you would be looking for in the spectrum?

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