Organic Chemistry Basics Questions for NDA

What is Organic Chemistry

Organic chemistry is the study of carbon compounds. Carbon is special because it can bond with itself (catenation) and form long chains, rings, and branches. This gives millions of different compounds. Almost all compounds found in living things are organic. The simplest organic compounds contain only carbon and hydrogen, called hydrocarbons.

• Organic compounds always contain carbon (C).
• Most also contain H, and many contain O, N, S, or halogens.
• Carbon forms 4 bonds always — this is key to its diversity.
• Catenation means carbon bonds to carbon to form chains or rings.
• Organic compounds generally have low melting points and are poor conductors of electricity.

Homologous Series

A homologous series is a family of organic compounds that share the same functional group and general formula, and each member differs from the next by a CH2 unit (molecular mass difference of 14). Members of the same series have similar chemical properties but gradually changing physical properties like boiling point and density. This concept is a favorite in NDA for identifying compound families.

• Each successive member differs by CH2 (14 mass units).
• Same functional group means same chemical reactions.
• Boiling point increases as chain length increases.
• General formula helps identify the series — e.g., CnH2n+2 for alkanes.
• First member of alkanes is methane (CH4), alkenes is ethene (C2H4), alkynes is ethyne (C2H2).

Functional Groups

A functional group is an atom or group of atoms that gives an organic compound its characteristic chemical properties. The rest of the molecule (the carbon chain) is mostly inactive. NDA frequently asks you to identify a compound class from its functional group or structural formula. Memorize the name, symbol, and compound class for each.

• Hydroxyl group -OH: alcohols (e.g., ethanol C2H5OH).
• Carboxyl group -COOH: carboxylic acids (e.g., acetic acid CH3COOH).
• Aldehyde group -CHO: aldehydes (e.g., formaldehyde HCHO).
• Ketone group -CO- (between two carbons): ketones (e.g., acetone CH3COCH3).
• Amino group -NH2: amines (e.g., methylamine CH3NH2).
• Halide group -X (F, Cl, Br, I): haloalkanes (e.g., chloroform CHCl3).

Types of Hydrocarbons

Hydrocarbons are compounds of only carbon and hydrogen. They are divided into saturated (only single bonds, alkanes) and unsaturated (double or triple bonds, alkenes and alkynes). There is also the special class of aromatic hydrocarbons like benzene that have a ring structure with alternating bonds. NDA often asks about reactivity trends and types of reactions each class undergoes.

• Alkanes: saturated, undergo substitution reactions, not very reactive.
• Alkenes: one double bond, undergo addition reactions, more reactive than alkanes.
• Alkynes: one triple bond, most reactive among the three, also addition reactions.
• Benzene (C6H6): aromatic, undergoes substitution not addition — this is a common trick question.
• Unsaturated compounds decolourise bromine water — used as a test for double/triple bonds.
• Methane burns with a blue flame; ethyne (acetylene) used in welding torches.

IUPAC Nomenclature Basics

IUPAC naming gives every organic compound a systematic name. For NDA, you need to know prefixes for carbon chain length and how to identify the parent chain. The name has three parts: prefix (substituents), root (chain length), and suffix (functional group).

• Carbon chain prefixes: Meth(1), Eth(2), Prop(3), But(4), Pent(5), Hex(6).
• Suffix for alkane: -ane, alkene: -ene, alkyne: -yne.
• Alcohol suffix: -ol, carboxylic acid suffix: -oic acid, aldehyde: -al, ketone: -one.
• Always number carbon chain from the end closest to the functional group.
• Common name vs IUPAC: Acetylene = Ethyne, Acetone = Propanone, Acetic acid = Ethanoic acid.

Important Organic Compounds for NDA

Certain compounds appear directly in NDA questions by name, use, or property. These are high-value memorization items and have appeared in previous year questions repeatedly.

• Methanol (CH3OH): wood spirit, highly toxic, used as fuel and solvent.
• Ethanol (C2H5OH): drinking alcohol, used as antiseptic and solvent.
• Acetic acid (CH3COOH): present in vinegar (4-8% solution).
• Formaldehyde (HCHO): used to preserve biological specimens (formalin = 40% solution).
• Chloroform (CHCl3): earlier used as anaesthetic, now used as solvent.
• DDT: organochlorine pesticide, persistent in environment — banned in many countries.
• Urea (NH2CONH2): first organic compound synthesized in lab by Wohler in 1828 — important historical fact.

• Confusing alkene (CnH2n) with cycloalkane — both have the same general formula but cycloalkanes have no double bond. NDA can test this indirectly.
• Thinking benzene undergoes addition reactions like alkenes — it does NOT. Benzene undergoes substitution despite having double bonds, due to its aromatic stability.
• Mixing up aldehyde and ketone: aldehyde has -CHO at the END of a chain, ketone has C=O in the MIDDLE. Acetone is a ketone, not an aldehyde.
• Confusing methanol and ethanol properties: methanol is poisonous (causes blindness/death), ethanol is the drinkable one. NDA asks about their uses.
• Forgetting that Wohler synthesized urea (an organic compound) from ammonium cyanate (inorganic) — this disproved the vital force theory and is a common fact-based question.

• Carbon chain lengths mnemonic: My Entire Property Belongs Properly Harvested — Meth, Eth, Prop, But, Pent, Hex.
• Functional group trick HACK: Alcohols Have One hydrogen on oxygen (-OH), Acids Have Two oxygens (-COOH), Aldehydes Have a Carbon with H and double O at the End (-CHO).
• Reactivity order of hydrocarbons: Alkynes > Alkenes > Alkanes. Think Triple beats Double beats Single — more bonds to break means more reactive.
• Bromine water test: Unsaturated compounds (alkenes, alkynes) DECOLOURISE bromine water. Remember: Double/triple bond = Decolourises. Single bond (alkane) = Does NOT.

• NDA typically asks 2-4 direct questions on organic chemistry basics per paper. These are usually one-liner fact questions: identifying functional groups, naming compounds, or matching uses of organic compounds.
• Homologous series and functional group identification are the highest frequency sub-topics. Prepare a simple table: series name, general formula, functional group, example compound.
• Common name to IUPAC name conversions appear regularly: Acetylene to Ethyne, Acetic acid to Ethanoic acid, Acetone to Propanone. Make a flashcard list of 10 such pairs.
• Historical and applied facts score easy marks: Wohler and urea synthesis, vinegar containing acetic acid, formalin for preservation, ethanol as antiseptic — these are direct one-mark questions.
• Do not spend more than 45-50 seconds per organic chemistry question. These are factual and you either know it or you do not. Skip and return if unsure rather than wasting time.