৪৯তম বিসিএস ⎯ রসায়ন [৫৩১]

2,3-butanediol (meso) → Achiral due to internal plane of symmetry.

So the right answer is B

Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel.

Fundamental criterion of chirality is non-superimposability. Presence of  stereogenic carbon atoms can't ensure chirality all the time (Ex: Meso Compound)
কাইরালিটির আবশ্যকীয় শর্ত হল দর্পন প্রতিবিম্ব পরস্পরের উপর অসমভাবে আপতিত হওয়া। স্টেরিওজেনিক কার্বন পরমাণুর উপস্থিতি সর্বদা কাইরালিটি নিশ্চিত করতে পারে না। (যেমন: Meso Compound).

So the right answer is D.

Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel.

A molecule that belongs to the D2d point group possesses
1. a highest-order rotation-reflection axis (S4) 
2.  two perpendicular C2 axes and
3. two perpendicular diagonal mirror planes (σd) that are bisected by the S4 axis.
A classic example is the allene molecule (H2C=C=CH2)

So the right answer is D.

Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel.

1,1′-bi-2-naphthol (BINOL) is an organic molecule with axial chirality, meaning its chirality arises from restricted rotation around a single bond, not from a traditional chiral center. (BINOL হল একটি জৈব অণু যার অক্ষীয় কাইরালিটি রয়েছে, যার অর্থ এর কাইরালিটি একটি একক বন্ধনের চারপাশে সীমিত ঘূর্ণন থেকে উদ্ভূত হয়, কাইরাল কেন্দ্র থেকে নয়।)

So the right answer is C

Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel.

2,3,4-trihydroxyglutaric acid  has two chiral carbon atoms, which leads to a total of four stereoisomers, including a meso form. (2,3,4-trihydroxyglutaric অ্যাসিডে দুটি কাইরাল কার্বন পরমাণু থাকে, যা মোট চারটি স্টেরিওআইসোমার তৈরি করে, যার মধ্যে একটি মেসো ফর্মও রয়েছে।)

So the right answer is  C
Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel.

The chirality of allenes arises from their  non-planar geometry due to the perpendicular alignment of the two pi systems. This geometry creates a chiral axis rather than a chiral center, which makes the molecule chiral when the two terminal carbons each bear two different substituents due to restricted rotation around C=C double bond

দুটি উল্লম্ব পাই সিস্টেমের কারণে অ্যালি নের কাইরালিটির  উদ্ভব ঘটে। এর কাইরাল কেন্দ্রের পরিবর্তে একটি কাইরাল অক্ষ তৈরি থাকে, যা C=C ডাবল বন্ডের চারপাশে সীমিত ঘূর্ণনের কারণেঅণুকে কাইরাল করে তোলে। 

So the right answer is D

Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel.

In conformationally restricted biphenyls, optical activity occurs when axial chirality is present due to steric hindrance from bulky ortho substituents, which prevents free rotation about the bond connecting the two phenyl rings, leading to non-superimposable mirror images (enantiomers) in the absence of any plane of symmetry. (যখন দুটি ফিনাইল রিংকে সংযুক্ত বন্ধনের চারপাশে মুক্ত ঘূর্ণনকে বাধা দেয় বা  অর্থো সাবস্টিটিউন্টের স্টেরিক বাধার কারণে অক্ষীয় কাইরালিটি উপস্থিত থাকে, তখন কাইরালিটির উদ্ভব ঘটে , যার ফলে অসমভাবে আপতিত দর্পণ প্রতিবিম্ব তৈরি হয়।)

So the right answer is B.

Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel.

Atropisomerism is a type of axial chirality in which stereoisomers arise from restricted rotation about a single bond, typically a biaryl bond, due to steric hindrance from bulky groups. (Atropisomerism হল এক ধরণের অক্ষীয় কাইরালিটি যেখানে স্টেরিও আইসোমারগুলি একটি একক বন্ধনের চারপাশে সীমিত ঘূর্ণন থেকে উদ্ভূত  হয়, সাধারণত বড় আকৃতির মূলকের স্টেরিক বাধার কারণে ঘটে।) 
So the right answer is C

Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel.

Planar chirality is a type of molecular chirality where the chirality originates from the arrangement of substituents relative to a chiral plane, rather than a chiral center or axis. (Planar chirality হল এক ধরণের আলোক সমাণুতা যেখানে কাইরালিটি একটি কাইরাল কেন্দ্র বা অক্ষের পরিবর্তে একটি কাইরাল সমতলের সাপেক্ষে মূলকগুলির বিন্যাস থেকে উদ্ভূত হয়।)
Example: substituted ferrocenes, such as 1-ethyl-2-methylferrocene, and certain cyclophanes, like PhanePhos, cavicularin, certain metallocenes and cycloalkenes

So the right answer is A
Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel.

Optical Rotatory Dispersion curves are plots of a chiral compound's optical rotation (α) as a function of wavelength (λ), revealing its stereochemical properties. (Optical Rotatory Dispersion কার্ভ হল তরঙ্গদৈর্ঘ্য (λ) এর ফাংশন হিসেবে একটি আলোক সক্রিয় যৌগের অপটিক্যাল রোটেশন (α) এর গ্রাফ।)


Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel.

In an ORD (Optical Rotatory Dispersion) curve, the sharp change in rotation near an absorption band corresponds to the Cotton Effect. The Cotton Effect region typically shows a characteristic S-shape, with a peak and a trough (or vice versa) around the absorption band. (ORD গ্রাফে একটি শোষণ ব্যান্ডের কাছাকাছি অঞ্চলে ঘূর্ণনের তীব্র পরিবর্তন Cotton Effect এর সাথে মিলে যায়। Cotton Effect অঞ্চলটি সাধারণত S-আকৃতি দেখায় যেখানে শোষণ ব্যান্ডের চারপাশে একটি শীর্ষ এবং একটি খাঁজ থাকে।)

Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel

Optical Rotatory Dispersion (ORD) provides information on chiral molecules even without chromophores, such as saccharides. It can be used to measure the chirality of non-absorbing samples and the determination of absolute configuration.

So the right answer is  B
Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel.

ORD measures dispersion of rotation; CD measures differential absorption of circularly polarized light.
Mathematically, CD is proportional to the derivative of the ORD curve near absorption.

So the right answer is C
Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel

CD is sharper and more reliable near absorption regions, while ORD provides broader dispersion data.

So the right answer is C
Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel

IV is Optically active.
I & II do not have chiral carbon. III is not optically active as it is a meso compound.

So the right answer is  C

Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel.

The Cotton effect is the characteristic anomaly in optical rotation close to an absorption band, classically tracked in ORD (with the corresponding CD signal in circular dichroism).
 কটন ইফেক্ট হলো শোষণ ব্যান্ডের কাছাকাছি অপটিক্যাল ঘূর্ণনের বিশেষ বিচ্যুতি, যা সাধারণত ORD-এ দেখা যায় 
So the right answer is C

Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel

Chiral chromophores interact differently with left vs. right circularly polarized light, giving rise to ORD/CD features including the Cotton effect near an absorption.
কাইরাল ক্রোমোফোর LCPL & RCPL এর  সঙ্গে ভিন্নভাবে মিথস্ক্রিয়া করে; এর ফলেই শোষণ ব্যান্ডের কাছে ORD/CD-তে কটন ইফেক্ট দেখা যায়।

So the right answer is  B

Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel

In ORD, a positive Cotton effect shows a trough (minimum) then a crest (maximum) across the band; the corresponding CD shows positive Δε in that region.

So the right answer is A

Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel

Enantiomers are non-superimposable mirror images of chiral molecules
Homomers are identical compounds that can form different configurations but are chemically equivalent in all respect.
Diastereomers  are not mirror images of each other and are non-superimposable
Identical compounds are exactly same in structure and properties.

So the right answer is A
Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel.

A plain curve occurs when there are no absorption bands in the measured region, showing smooth dispersion. 

So the right answer is A

Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel.

The 3D arrangement/absolute configuration around the chromophore governs the sign through exciton-coupling or octant-type rules.
ক্রোমোফোরের চারপাশের অ্যাবসোলিউট কনফিগারেশন ও ত্রিমাত্রিক বিন্যাসের কারণে কটন ইফেক্টের চিহ্ন নির্ধারিত হয় 

So the right answer is C

Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel

The sign and shape of the Cotton effect in ORD/CD are used widely to determine absolute configuration of stereogenic centers. (ORD/CD-তে কটন ইফেক্টের চিহ্ন ও আকার দেখে কাইরাল কেন্দ্রের অ্যাবসোলিউট কনফিগারেশন নির্ধারণ করা হয়।)

So the right answer is C

Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel

 Circular birefringence means n_L≠n_R ​; the phase difference between LCP and RCP rotates the polarization plane.

So the right answer is B
Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel.

Different phase velocities for LCP and RCP rotate the plane-polarized light—this is optical rotation.

So the right answer is B

Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel

 θ∝(n_L−n_R)* l * c; 
 where (n_L−n_R) is the difference in refractive indices for LCP and RCP light,
             l is the path length/thickness    and 
              c is the concentration. 

So the right answer is B

Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel.

Their molecular structure lacks mirror symmetry. This property arises because linearly polarized light is composed of two circularly polarized components (left and right) that travel at different speeds in chiral media, causing a phase shift  (n_L≠n_R) that rotates the overall linear polarization of the light.  

So the right answer is  B

Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel

Optical rotatory power increases with-
1. greater concentration of the substance
2.longer path length 
3. shorter wavelengths of light and
4. higher temperatures for some materials

So, Rotation ∝ l×c×[α]

So the right answer is C
Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel

The Born–Kuhn model differs in that it employs two instead of one charged particle and that these are coupled to each other. Coupling of transition dipoles in chiral geometry gives CD/ORD signals. 

So the right answer is B
Source: Relevant websites

Dissymmetric means-
1. Simple axis may or may not be present
2. Alternating axis absent
3. Usually opyically active

So the right answer is C

Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel

CIP Rule: Compare substituents atom-by-atom; higher atomic number gets higher priority.
 
So the right answer is B
Source: Bahl & Bahl/Class lecture number 6

Diastereomers: are stereoisomers with the same chemical formula and connectivity, that are not mirror images of each other and are non-superimposable

So the right answer is C
Source: Class lecture number 6

Nitrogen inversion makes simple amines non-resolvable into stable enantiomers (a racemic mixture), as the inversion process rapidly interconverts mirror images

So the right answer is B
Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel

Kramers-Kronig relations are used to relate the CD spectrum  to the circular birefringence spectrum of a chiral substance.

So the right answer is B
Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel

Resolution of a racemate via salts requires a racemic mixture, an enantiopure chiral resolving agent (a specific chiral acid or base), and the ability to form diastereomeric salts with different solubilities.
কাইরাল অ্যাসিড/ক্ষারের সাথে ডায়াস্টেরিওমেরিক লবণ গঠন করে দ্রবণীয়তার তারতম্যে পৃথক করা যায়।

So the right answer is B
Source: Text book of organic chemistry (B.S. Bahl & Arun Bahl)/See class lecture number 6

Mutarotation is the change in optical rotation of a chiral molecule, like a sugar, in solution, occurring as the different anomeric forms (e.g., α and β anomers) of the sugar interconvert to reach a new equilibrium.

So the right answer is B

Source: Text book of organic chemistry (B.S. Bahl & Arun Bahl)/Any text book from HSC level

Two molecules are said to be identical if they have the same connectivity, same configuration at each stereocenter and spatial arrangement- even if drawn differently.

So the right answer is A
Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel

A conformer pair becomes "resolvable enantiomers" when the two different conformational arrangements become distinct, non-superimposable mirror images of each other at a specific point, allowing for their separation into pure forms. This process, known as enantiomeric resolution. Here, Slow interconversion is key.

So the answer is B
Source: Relevant websites

Natural optical activity is an inherent property of certain molecular structures, particularly chiral ones, that doesn't require an external magnetic field,
 প্রাকৃতিক ঘূর্ণন অণুর কাইরালিটি থেকে আসে; ফ্যারাডে রোটেশনে বাহ্যিক চৌম্বক ক্ষেত্র লাগে।
so the answer is C
Source: Relevant websites

স্যাচুরেশন না হলে ΔA (intensity) l (path length) ও c (concentration)-এর সঙ্গে বাড়ে।
So the answer is B

Source: Relevant websites

So the answer is B
See Class lecture

In pyranoses, the anomeric effect favors the axial orientation of electronegative substituents at the anomeric carbon.

So the answer is B
Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel

The benzene sector rule predicts the sign of the Cotton Effect (CE) for the benzene chromophore in chiral molecules.

So the answer is B
Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel

An exciton couplet arises from through-space exciton coupling between two chromophores in a chiral environment. Their electronic transition dipole moments (TDMs) interact, causing their absorption bands to split and creating a characteristic circular dichroism 

So the answer is B
Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel

যখন নাইট্রোজেনের সাথে ৪টা ভিন্ন অ্যালকাইল গ্রুপ যুক্ত থাকে তখন নাইট্রোজেনের কোন মুক্তজোড় ইলেকট্রন থাকে না, ফলে ইনভার্সন হয় না। ফলে যৌগটি স্থিতিশীল ও আলোক সক্রিয় হয়।

So the answer is B

Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel

The factors primarily influences the shape of an ORD curve:
1. Chiral Centers
2. Absolute Configuration
3. Functional Groups (Chromophores)
4. Wavelength
5. Molecular Structure

So the right answer is C

Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel

Stereogenic center থাকলেও আলোক সক্রিয়তা নাও দেখাতে পারে। (যেমন: meso যৌগ)

So the right answer is A
Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel.

So, (+) glyceraldehyde and (–) glyceraldehyde are enantiomers

Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel

1,2-disubstituted cyclopropanes show cis/trans arrangement. As a result, Chirality depends on cis/trans arrangement of substituents.

So the right answer is A
Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel

A meso compound is an organic molecule that possesses at least two stereocenters but is achiral and optically inactive because it has an internal plane of symmetry. 

So the right answer is B
Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel

the presence of a center of inversion, a plane of symmetry, or any improper rotation axis (Sn) makes a molecule achiral.

So the right answer is C

Source: Stereochemistry Of Carbon Compounds By Ernest L. Euel