Problem 168 - A Complete Resource Book in Chemistry for JEE Main

Question

Match the following Column-I (a) C=CC(C)I (b) C=CC(C)(c1cccc([N+](=O)[O-])c1)C(C)C (c) CC(C)C (Singlet) (d) CC(=O)C(F)C(C)=O Column-II (p) resonance (q) \(+\mathrm{I}\) effect (r) \(-\) I effect (s) hyper conjugation (t) intermediate is sp \(^{2}\) hybridized

Step-by-Step Solution

Answer

(a) - r, (b) - s, (c) - t, (d) - p.

Step 1: Analyze Compound Structures

Identify the key features and functional groups in each compound using the given SMILES notations. For example, compound (a) "C=CC(C)I" contains an alkene (C=C) with an iodine atom, compound (b) "C=CC(C)(c1cccc([N+](=O)[O-])c1)C(C)C" has an alkene connected to a nitrobenzene and two isopropyl groups, compound (c) "CC(C)C" describes an alkane with a singlet referring to empty p-orbital or lone pair, and compound (d) "CC(=O)C(F)C(C)=O" is a diketone with fluorine.

Step 2: Match Features with Effects

- For compound (a), the iodine (I) can exhibit the -I effect due to its electronegativity. - Compound (b) can show hyper conjugation due to the structure of the alkene in conjunction with nearby isopropyl groups. - Compound (c), being a simple alkane, relates to the I effect, particularly due to carbocation formation tendency if relevant. - Compound (d) features two carbonyl groups which are known for resonance.

Step 3: Identify Hybridization and Intermediate States

Determine if there is a likely formation of any intermediates or potential resonance structures: - In (a), the carbon involved in the double bond will have potential for resonance. - In (b), the central carbon shares connections that might result in hyper conjugation. - Compound (c) is a singlet, often meaning an intermediate with sp² hybridization could form. - For (d), the presence of resonance could involve intermediates, likely sp² hybridized, due to resonance with the carbonyl groups.

Step 4: Match Columns Using Effects and Hybridization

Based on the analysis: - (a) relates to I effect (r), due to Iodine's electronegativity. - (b) involves hyper conjugation (s), due to its structure. - (c) relates to a potential scenario where an intermediate is sp² hybridized (t), typical with a singlet status. - (d) demonstrates resonance (p) with its carbonyl groups.

Key Concepts

I Effect

The I effect, also known as the inductive effect, is an important concept in organic chemistry. It describes how the electronegativity of atoms, particularly those that are adjacent to a carbon chain, can affect the electron distribution within molecules. The I effect can be either positive ( +I ) or negative ( -I ), depending on whether the atom is donating electrons through the sigma bond system or withdrawing them.

• A positive I effect occurs when there is electron donation. Typically seen with alkyl groups pushing electrons towards a reactive center, stabilizing positive charges like carbocations.
• A negative I effect takes place when an atom like iodine, which has high electronegativity, pulls electrons away. This often increases the electron deficiency of the rest of the molecule.

Understanding this effect helps explain the reactivity and stability of various organic compounds.

Hyper Conjugation

Hyper conjugation is a stabilizing interaction that results from the interaction of electrons in a sigma bond (usually C-H or C-C) with an adjacent empty p-orbital or a π orbital to form an extended molecular orbital. This phenomenon is sometimes referred to as "no-bond resonance."

• The hyper conjugation effect can explain the stability of alkenes and carbocations. In alkenes, the overlap between the C-H bonds and adjacent π bonds disperses the electron density, stabilizing the molecule further.
• For carbocations, hyper conjugation allows for delocalization of the positive charge over several adjacent carbon atoms, enhancing stability.

In compound (b), hyper conjugation is critical due to the interaction of the isopropyl groups with the double bond, which enhances the stability of the compound.

Resonance

Resonance is a concept used to describe delocalized electrons within certain molecules where the electron distribution can be represented by several contributing structures. It is a powerful tool in understanding the stability of compounds.

• In resonance, no single structure can depict the true form of the molecule. Instead, a weighted average (resonance hybrid) of multiple structures represents the actual arrangement of electrons.
• The presence of conjugated systems, such as alternating single and double bonds, often indicates possible resonance.
• In compound (d), resonance arises due to the presence of two carbonyl groups and the fluorine atom interacting through the molecular structure, facilitating electron delocalization.

This effect allows for significant stabilization of molecules by distributing electron density over a larger volume.

sp² Hybridization

sp² hybridization is a concept within chemistry that describes the type of hybrid orbitals used by atoms in compounds. An atom undergoes sp² hybridization when one s orbital mixes with two p orbitals, forming three equivalent sp² hybrid orbitals.

• sp² hybridized atoms typically adopt a planar triangular geometry with bond angles of 120°, making them ideal for forming double bonds, characteristic in alkenes.
• For compounds like (c), the mention of a singlet state often implies the possibility of transient sp² hybridization. Singlet implies either an empty p-orbital or a lone pair that could be reorganized into an sp² planar form, crucial for intermediate states.

Understanding sp² hybridization clarifies molecular shapes and reactivity patterns in various organic and inorganic compounds.