Organic Basics - Class 11 Chemistry

Organic Chemistry Basics

Overview: Tetravalence of Carbon, Shape of Organic Compounds, IUPAC Nomenclature, Isomerism, and Fundamental Concepts (Inductive, Resonance, Hyperconjugation).

1. IUPAC Nomenclature

Systematic way of naming organic compounds. Format: Prefix + Word Root + Suffix.

Word Root: Meth (1), Eth (2), Prop (3)...
Primary Suffix: ane (-), ene (=), yne (triple).
Secondary Suffix: Functional Group (ol, al, one, oic acid).
Priority Order: COOH > SO3H > COOR > COCl > CONH2 > CN > CHO > C=O > OH > NH2 > C=C > C≡C > R.

2. Isomerism

Same molecular formula, different properties.

Structural: Chain, Position, Functional, Metamerism.
Stereo: Geometrical (Cis-Trans), Optical (Enantiomers).

3. Electronic Effects

Inductive Effect (I)

Permanent displacement of sigma electrons along carbon chain. (-I: halogen, NO2; +I: alkyl).

Resonance Effect (R/M)

Delocalization of pi electrons. (+M: OH, NH2; -M: NO2, CHO).

Hyperconjugation (H)

Delocalization of sigma electrons of C-H bond of alkyl group directly attached to unsaturated system or carbocation (Baker-Nathan Effect).

4. Reaction Intermediates

Carbocation (C+): sp2, planar (e.g. CH3+). Stability: 3° > 2° > 1°.
Carbanion (C-): sp3, pyramidal. Stability: 1° > 2° > 3°.
Free Radical (C·): sp2, planar. Stability: 3° > 2° > 1°.

5. Purification & Analysis

Distillation: Difference in BP.
Chromatography: Differential adsorption.
Lassaigne's Test: Detection of N (Prussian Blue), S (Violet/Black), Halogens.
Kjeldahl's Method: Estimation of N (as NH3).
Dumas Method: Estimation of N (as N2).

Numericals - Organic Basics

Numericals

IUPAC Name

Q1. Write IUPAC name of CH3-CH(OH)-CH2-COOH.

Principal functional group: -COOH (starts #1).

Numbering: C1(COOH)-C2-C3(OH)-C4(CH3).

Substituent: Hydroxy at C3.

Name: 3-Hydroxybutanoic acid.

Hybridization

Q2. State hybridization of C atoms in CH2=C=CH2 (Allene).

Terminal C's: Involved in 1 double bond → sp2.

Middle C: Involved in 2 double bonds → sp.

Answer: sp2 - sp - sp2.

Isomerism

Q3. Write total structural isomers for C4H10O (Alcohol + Ether).

Alcohols (4): 1-Butanol, 2-Butanol, Isobutyl alcohol, t-Butyl alcohol.

Ethers (3): Diethyl ether, Methyl propyl ether, Methyl isopropyl ether.

Total = 7.

Stability of Intermediates

Q4. Arrange in stability: (CH3)3C+, (CH3)2CH+, CH3CH2+.

Stability of Carbocation: 3° > 2° > 1°.

(CH3)3C+ (9 alpha H) > (CH3)2CH+ (6 alpha H) > CH3CH2+ (3 alpha H).

Reason: Hyperconjugation and +I effect.

Quant Analysis (Dumas)

Q5. 0.3g organic compound gave 50ml N2 at 300K, 700mm. Calc %N. (Aq tension = 15mm).

P_dry = 700 - 15 = 685 mm.

V_stp = (P V 273) / (T 760) = (685 × 50 × 273) / (300 × 760) = 41.01 ml.

Mass N2 = (41.01 / 22400) × 28 = 0.051 g.

%N = (0.051 / 0.3) × 100 = 17.1%.

Quant Analysis (C & H)

Q6. 0.2g compound gave 0.3g CO2 and 0.1g H2O. Calc %C.

%C = (12/44) × (Mass CO2 / Mass Comp) × 100

%C = (12/44) × (0.3 / 0.2) × 100

%C = 0.2727 × 1.5 × 100 = 40.9%.

IUPAC

Q7. Name: Benzene ring with -OH and -NO2 at para.

Parent is Phenol (OH priority > NO2).

Numbering starts from OH=1. NO2 at 4.

Name: 4-Nitrophenol (or p-Nitrophenol).

Sigma Pi bonds

Q8. Count sigma and pi bonds in Toluene (C6H5-CH3).

Ring: 6 C-C (3 single, 3 double). 3 pi bonds.

C-H bonds on ring: 5.

Methyl group: 1 C-C bond to ring, 3 C-H bonds.

Total Sigma: 6+5+1+3 = 15. Total Pi: 3.

Kjeldahl

Q9. Ammonia from 0.5g compound neutralized 10ml of 1M H2SO4. Calc %N.

%N = (1.4 × Molarity × Vol(Used) × Basicity) / Mass

Basicity of H2SO4 = 2. So Normality = 2M.

%N = (1.4 × 2 × 10) / 0.5

%N = 28 / 0.5 = 56%.

Nucleophile vs Electrophile

Q10. Identify Electrophile: NH3, AlCl3, H2O, CN-.

Electrophile: Electron seeking (Positive or incomplete octet).

NH3 (Lone pair - Nuc). H2O (Lone pair - Nuc). CN- (Negative - Nuc).

AlCl3 (Incomplete octet of Al - Lewis Acid).

Ans: AlCl3.

Formulas & Facts - Organic Basics

Equations & Formulas

Analysis	Formula
% Carbon	12/44 x (mCO2 / M) x 100
% Hydrogen	2/18 x (mH2O / M) x 100
% Nitrogen (Dumas)	28/22400 x (V_stp / M) x 100
% Nitrogen (Kjeldahl)	1.4 x N x V / M
% Halogen (Carius)	(At.wt / Mol.wt AgX) x (mAgX / M) x 100
% Sulfur	32/233 x (BaSO4 / M) x 100
Number of Isomers	2^(n-1) + ... (varies)

50 NEET Facts

Key points for Organic Chemistry.

1. Vital Force Theory Berzelius proposed organic compounds can't be synthesized artificially.

2. Wohler's Synthesis Synthesized Urea (NH2CONH2) from Ammonium Cyanate, disproving Vital Force Theory.

3. Catenation Self-linking property of C atoms. C > Si > Ge.

4. Hybridization in Organic Single bond (sp3), Double bond (sp2), Triple bond (sp).

5. Homologous Series Differs by -CH2- unit (14u mass). Similar chemical properties.

6. Functional Group Atom/group determining chemical properties (e.g., -OH, -COOH).

7. Metamerism Isomerism due to different alkyl mechanism on either side of functional group (Ethers, Ketones).

8. Tautomerism Functional isomers existing in dynamic equilibrium (Keto-Enol). Involves migration of H+.

9. Inductive Effect Permanent. operates through sigma bonds. Decreases with distance.

10. Electromeric Effect Temporary. Involves pi electrons. Occurs only in presence of attacking reagent.

11. Hyperconjugation No bond resonance. Stabilizes carbocations and alkenes. Depends on number of alpha-H.

12. Mesomeric Effect Resonance effect. Permanent delocalization.

13. Carbocation Stability 3° > 2° > 1° > Methyl. (Due to +I and Hyperconjugation).

14. Carbanion Stability Methyl > 1° > 2° > 3°. (Destabilized by +I).

15. Free Radical Stability 3° > 2° > 1°. (Similar to carbocation).

16. Electrophile Electron lover. +ve charge or neutral with incomplete octet (BF3, AlCl3).

17. Nucleophile Nucleus lover. -ve charge or neutral with lone pair (NH3, H2O).

18. Homolytic Fission Forms free radicals. Occurs in presence of Light/Heat/Peroxide (HELPR).

19. Heterolytic Fission Forms ions (Cation + Anion). Occurs in polar solvent.

20. Lassaigne's Test Na Used to convert Covalent N, S, Halogens into Ionic form (NaCN, Na2S, NaX).

21. Test for N Prussian Blue color (Fe4[Fe(CN)6]3).

22. Test for S Sodium nitroprusside -> Violet color.

23. Beilstein Test Green flame with Cu wire. Detects halogens (but urea also gives +ve).

24. Kjeldahl Limit Not valid for N in ring (Pyridine), Nitro (-NO2), Azo (-N=N-).

25. Chromatography Rf Retardation factor. Distance moved by substance / Distance by solvent. Always <= 1.

26. Steam Distillation For substances immiscible with water and steam volatile (Aniline, Nitrobenzene).

27. Vacuum Distillation For substances decomposing at BP (Glycerol).

28. Differential Extraction Separation using separating funnel based on solubility in organic solvent.

29. Geometrical Isomerism Restricted rotation (C=C). cis (same side), trans (opposite).

30. Dipole of isomers cis > trans (usually). cis-1,2-dichloroethene is polar. Trans is non-polar.

31. BP of isomers cis > trans (due to higher dipole).

32. MP of isomers trans > cis (due to better packing symmetry).

33. Chirality Non-superimposable mirror image. Carbon with 4 different groups.

34. Enantiomers Pair of optical isomers. Rotate light in opp specific directions.

35. Racemic Mixture 50:50 mix of enantiomers. Optically inactive (External compensation).

36. Meso Compound Has chiral centers but optically inactive due to plane of symmetry (Internal compensation).

37. Conformations Infinite spacial arrangements by rotation around C-C bond (Ethane: Staggered, Eclipsed).

38. Staggered Stability More stable than Eclipsed (min repulsion). Dihedral angle 60 deg.

39. Benzene Shape Planar, Hexagonal. All angles 120. sp2 C. Aromatic.

40. Huckel's Rule (4n + 2) pi electrons. Condition for aromaticity.

41. Anti-aromatic 4n pi electrons. Unstable.

42. Ortho-Para directing Activators (donate e-). -OH, -NH2, -CH3, -Cl (exception: deactivator but OP).

43. Meta directing Deactivators (withdraw e-). -NO2, -COOH, -CHO, -CN.

44. Strongest Acid Picric Acid (2,4,6-trinitrophenol). ~HCl strength.

45. Acidity Order RCOOH > Phenol > H2O > ROH > Alkyne > NH3 > Alkene > Alkane.

46. Basicity Order Amines > NH3. (In gas: 3>2>1. In water: 2>1>3 for methyl).

47. E1 vs E2 Elimination Unimolecular (via Carbocation). Bimolecular (Single step).

48. SN1 vs SN2 SN1 (2 steps, Racemization, 3 degree). SN2 (1 step, Inversion, 1 degree).

49. Priority of C=C vs Triple Double bond gets priority over Triple bond in numbering if positions equivalent.

50. IUPAC name of Neopentane 2,2-Dimethylpropane.

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