Q.60 Amongst the molecules given below, the total number of molecules that have at
least one sp2 hybridized atom is __________.
C6H6, NO2, BF3, H2O2, SO2, C2H2, L–Tryptophan
C6H6, NO₂, BF₃, H₂O₂, SO₂, C₂H₂, and L-Tryptophan represent key molecules in CSIR NET Life Sciences exams testing hybridization concepts. Six of these seven molecules contain at least one sp² hybridized atom. The answer is 6.
Hybridization Rules
Hybridization depends on steric number (sigma bonds + lone pairs on central atom). Sp² hybridization occurs with steric number 3, forming three sp² orbitals and one unhybridized p orbital for pi bonding. Examples include trigonal planar geometry in BF₃ and resonance structures in benzene.
Molecule Analysis
Each molecule undergoes detailed Lewis structure and steric number evaluation.
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C₆H₆ (Benzene): All six carbons show steric number 3 (three sigma bonds), confirming sp² hybridization. Pi electrons delocalize in the aromatic ring.
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NO₂ (Nitrogen Dioxide): Central N has steric number 3 (two sigma bonds to O, one lone pair), sp² hybridized. Bent geometry arises from resonance.
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BF₃ (Boron Trifluoride): Central B has steric number 3 (three sigma bonds to F), sp² hybridized. Trigonal planar with empty p orbital.
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H₂O₂ (Hydrogen Peroxide): Both O atoms have steric number 4 (two sigma bonds, two lone pairs), sp³ hybridized only.
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SO₂ (Sulfur Dioxide): Central S has steric number 3 (two sigma bonds to O, one lone pair), sp² hybridized. Bent with double bond character.
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C₂H₂ (Acetylene): Both C atoms have steric number 2 (one sigma bond to C, one to H), sp hybridized.
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L-Tryptophan: Contains indole ring with multiple sp² carbons (aromatic system, C=C, C=N). Carboxylic C also sp².
| Molecule | Central Atom(s) Steric Number | Hybridization | Has sp²? |
|---|---|---|---|
| C₆H₆ | C: 3 | sp² | Yes |
| NO₂ | N: 3 | sp² | Yes |
| BF₃ | B: 3 | sp² | Yes |
| H₂O₂ | O: 4 | sp³ | No |
| SO₂ | S: 3 | sp² | Yes |
| C₂H₂ | C: 2 | sp | No |
| L-Tryptophan | Ring C: 3, Carboxyl C: 3 | sp² | Yes |
CSIR NET Exam Tips
Focus on central atom steric numbers for small molecules; scan for aromatic rings or carbonyls in biomolecules like L-Tryptophan. Practice resonance structures for NO₂ and SO₂.
