This is the most important chapter for any medical or engineering aspirant—it is the “Alphabet” of the carbon world. If you master this, the rest of Organic Chemistry becomes a breeze.

The Language of Carbon: Mastering Organic Chemistry Basics

Organic Chemistry is not about memorizing thousands of reactions; it is about understanding Electronic Effects. Why does one molecule attack another? Why is one acid stronger than another? It all comes down to how electrons move within the carbon skeleton.

In this chapter, we explore IUPAC naming, the art of drawing 3D molecules on 2D paper, and the “Invisible Forces” (Inductive, Electromeric, Resonance, and Hyperconjugation) that dictate the fate of every organic reaction.

The Core Pillars of Organic Basics

1. IUPAC Nomenclature: The Universal Address

Every organic molecule has a unique name based on its structure.

• The Rule: Secondary Prefix + Primary Prefix + Word Root + Primary Suffix + Secondary Suffix.
• Priority: Functional Group > Double/Triple Bond > Substituents.

2. Isomerism: The Shape Shifters

Isomers are molecules with the same molecular formula but different arrangements.

• Structural: Different connectivity (Chain, Position, Functional, Metamerism).
• Stereoisomerism: Same connectivity, different 3D orientation (Geometrical and Optical).

3. Electronic Effects (The “Big Four”)

These effects explain why reactions happen:

• Inductive Effect (I): Permanent displacement of electrons along a sigma bond due to electronegativity.
• Resonance (R): Delocalization of pi electrons. This is the “Superpower” that stabilizes molecules like Benzene.
• Hyperconjugation (H): “No-bond resonance” involving sigma electrons of C-H bonds.
• Electromeric Effect (E): A temporary effect that happens only when a reagent attacks.

4. Cleavage of Bonds

• Homolytic: Each atom takes one electron, creating Free Radicals.
• Heterolytic: One atom takes both electrons, creating Carbocations (C+) or Carbanions (C-).

The Gauntlet: 10 Challenging Aptitude Questions

Question 1: The Priority naming

Write the IUPAC name for: CH3 – CH(OH) – CH2 – CO – CH3. Hint: Does the Alcohol or the Ketone get the priority?

Question 2: Stability of Carbocations

Arrange the following in increasing order of stability:

(CH3)3C+, (CH3)2CH+, CH3CH2+, CH3+. Explain using Inductive and Hyperconjugation effects.

Question 3: The Resonance Hybrid

Draw the resonating structures of the Nitrobenzene molecule. Does the NO2 group donate or withdraw electrons from the ring?

Question 4: Acidity Logic

Why is Chloroacetic acid (Cl-CH2-COOH) a stronger acid than Acetic acid (CH3-COOH)?

Question 5: Metamerism Mystery

Which of the following pairs exhibit metamerism?

1. CH3CH2OCH2CH3 and CH3OCH2CH2CH3
2. CH3CH2CH2OH and CH3CH(OH)CH3

Question 6: The Kjeldahl Method Calculation

In a Kjeldahl’s estimation of nitrogen, the ammonia evolved from 0.5g of an organic compound neutralized 10mL of 1M H2SO4. Calculate the percentage of nitrogen in the compound.

Question 7: Hyperconjugation in Alkenes

Which is more stable: But-1-ene or But-2-ene? Use the number of alpha-hydrogens to justify your answer.

Question 8: Nucleophile vs. Electrophile

Identify the nucleophile and electrophile in the following reaction:

CH3Br + OH- → CH3OH + Br-

Question 9: Chromatography Principle

In Thin Layer Chromatography (TLC), if compound A moves further up the plate than compound B, which compound is more strongly adsorbed to the stationary phase?

Question 10: The Lassaigne’s Test

In Lassaigne’s test for Nitrogen, a Prussian Blue color is obtained. What is the chemical formula of the complex responsible for this color?

Detailed Explanations & Solutions

1. IUPAC Naming

Ketone (>CO) has higher priority than Alcohol (-OH). The OH becomes a prefix “hydroxy”. Numbering starts from the Ketone side.

Result: 4-Hydroxypentan-2-one.

2. Carbocation Stability

Tertiary (3°) > Secondary (2°) > Primary (1°) > Methyl.

3° has 9 alpha-hydrogens for hyperconjugation and 3 electron-donating methyl groups (+I effect).

Result: CH3+ < CH3CH2+ < (CH3)2CH+ < (CH3)3C+.

3. Nitrobenzene Resonance

The -NO2 group is a -R (Electron Withdrawing) group. It pulls electron density out of the benzene ring, specifically from the ortho and para positions.

Result: Nitrobenzene is deactivated towards electrophilic attack.

4. Inductive Effect and Acidity

Chlorine is electronegative and shows the -I effect. It pulls electrons away from the O-H bond, making it easier for the H+ to leave.

Result: Cl-CH2-COOH is stronger because the -I effect stabilizes the carboxylate ion.

5. Metamerism

Metamerism occurs when there is a different distribution of carbon atoms on either side of a functional group (like -O-, -S-, or -CO-).

Result: Pair 1 (Diethyl ether and Methyl propyl ether) are metamers.

6. Nitrogen Calculation

10mL of 1M H2SO4 = 20 milliequivalents of Acid = 20 milliequivalents of NH3 = 20 milliequivalents of N.

Mass of N = (20 / 1000) * 14 = 0.28g.

% N = (0.28 / 0.5) * 100.

Result: 56%.

7. Alkene Stability

But-2-ene (CH3-CH=CH-CH3) has 6 alpha-hydrogens. But-1-ene (CH2=CH-CH2-CH3) has only 2 alpha-hydrogens.

Result: But-2-ene is more stable due to greater hyperconjugation.

8. Reactive Species

OH- is electron-rich and seeks a nucleus (Nucleophile). CH3Br has a partial positive charge on Carbon, making it electron-poor (Electrophile).

Result: Nucleophile = OH-; Electrophile = CH3Br.

9. TLC Logic

The stationary phase (silica) “holds back” the compound that is more strongly adsorbed. Since B moved less, it is held more tightly.

Result: Compound B is more strongly adsorbed.

10. Lassaigne’s Test

The Prussian Blue color is due to the formation of Ferriferrocyanide.

Result: Fe4[Fe(CN)6]3.

Pro-Tip: The “Effect Hierarchy”

When predicting stability or reactivity, always follow this priority: Resonance > Hyperconjugation > Inductive Effect. A molecule stabilized by resonance will almost always be more stable than one stabilized only by inductive effects!