Organic Chemistry Fundamentals: NMAT Chemistry Review

Why Organic Chemistry Matters in the NMAT

Organic chemistry in the NMAT is less about memorizing hundreds of named reactions and more about recognizing
patterns: how electrons move, why certain atoms attract electrons, and which structures are stable or unstable.
If you can read a structure, identify functional groups, and predict the “most likely” outcome, you can solve
many NMAT-style questions quickly. The exam often tests core ideas such as bonding, acidity/basicity, reaction
types, stereochemistry basics, and functional group transformations. This review focuses on those fundamentals
and the most test-relevant skills: interpreting line-angle formulas, ranking stability, predicting products,
and choosing the best reagent or condition.

Core Language of Organic Chemistry: Structures and Electron Movement

Organic chemistry is the chemistry of carbon compounds. Carbon forms four bonds and can create chains and rings,
leading to a huge variety of molecules. In NMAT questions, structures are commonly shown in line-angle (skeletal)
formulas. In these, each line represents a bond and each vertex represents a carbon unless labeled otherwise.
Hydrogens attached to carbons are omitted but understood to complete carbon’s valence of four.

A key skill is tracking electrons. Most organic reactions can be described by electron-rich species reacting with
electron-poor species. Electron-rich sites are often:

• Negatively charged atoms (e.g., O⁻, N⁻, halides in some contexts)
• Atoms with lone pairs (O, N, S, halogens)
• Pi bonds (C=C, C≡C, C=O)

Electron-poor sites are often:

• Positively charged atoms (carbocations, protonated heteroatoms)
• Polarized carbons attached to electronegative atoms (e.g., carbonyl carbon)
• Atoms that can accept electrons through empty orbitals (Lewis acids)

If you keep the “electron-rich attacks electron-poor” idea in mind, mechanisms become less mysterious.
Even when the NMAT does not require full arrow-pushing, this logic helps predict products and intermediates.

Bonding and Hybridization: sp, sp², sp³

Hybridization influences geometry, bond angles, and reactivity. You’ll frequently need to identify or compare
hybridization states.

• sp³: tetrahedral, ~109.5° (alkanes, single bonds)
• sp²: trigonal planar, ~120° (alkenes, carbonyl carbons)
• sp: linear, 180° (alkynes, nitriles)

More “s-character” means electrons are held closer to the nucleus. Therefore:

• sp is more electronegative than sp², which is more electronegative than sp³.
• C–H acidity increases with s-character: terminal alkyne (sp) H is more acidic than alkene (sp²) H, which is more acidic than alkane (sp³) H.

You don’t need exact pK_a values for NMAT, but you should know relative acidity trends.

Functional Groups You Must Recognize

NMAT organic chemistry questions often start with a structure. Fast functional group recognition is essential.
Common groups include:

• Alkanes (C–C single bonds): relatively unreactive
• Alkenes (C=C): undergo addition reactions
• Alkynes (C≡C): addition reactions; terminal alkynes can be deprotonated
• Aromatic rings (benzene): resonance-stabilized; electrophilic substitution
• Alcohols (R–OH): can be oxidized; can be converted into leaving groups
• Ethers (R–O–R): generally stable; can be cleaved under strong conditions
• Alkyl halides (R–X): key substrates for substitution/elimination
• Aldehydes (R–CHO) and ketones (R–CO–R): carbonyl chemistry
• Carboxylic acids (R–COOH): acidic; form derivatives
• Esters (R–COOR), amides (R–CONH₂/R–CONR₂), acid chlorides (R–COCl): carboxylic acid derivatives
• Amines (R–NH₂/R–NHR/R–NR₂): basic; nucleophilic

A quick NMAT strategy: circle (mentally) heteroatoms (O, N, halogens), identify carbonyls (C=O), and look for pi bonds.
These often determine the reaction behavior.

Isomerism Basics: Constitutional vs Stereoisomers

Isomers share the same molecular formula but differ in structure. Two main types are:

• Constitutional (structural) isomers: different connectivity (atoms connected differently).
• Stereoisomers: same connectivity, different 3D arrangement.

Stereoisomers can be:

• Geometric isomers (cis/trans or E/Z) in alkenes due to restricted rotation around the double bond.
• Enantiomers: non-superimposable mirror images (chirality).
• Diasttereomers: stereoisomers that are not mirror images.

At NMAT level, you should be comfortable recognizing when a carbon is chiral: a tetrahedral carbon attached to four
different substituents. A classic property difference: enantiomers have identical physical properties in achiral
environments except they rotate plane-polarized light in opposite directions and can behave differently in biological systems.

Polarity and Intermolecular Forces: Predicting Boiling Points and Solubility

NMAT may test physical properties: boiling point trends, solubility, and polarity. Intermolecular forces include:

• London dispersion: present in all molecules; increases with size and surface area.
• Dipole–dipole: in polar molecules.
• Hydrogen bonding: strong dipole interaction when H is bonded to N, O, or F, interacting with lone pairs on N/O/F.

General trends:

• Higher molecular mass and stronger intermolecular forces → higher boiling point.
• Alcohols usually have higher boiling points than comparable alkanes/ethers due to hydrogen bonding.
• “Like dissolves like”: polar/ionic compounds dissolve better in polar solvents (water); nonpolar compounds dissolve better in nonpolar solvents (hexane).

For solubility in water, small alcohols and amines can dissolve well, but increasing carbon chain length reduces solubility
because the hydrophobic portion dominates.

Acidity and Basicity in Organic Chemistry

A high-yield NMAT topic is ranking acidity/basicity. Organic acidity depends on stability of the conjugate base.
More stable conjugate base → stronger acid. Key stabilizing factors:

• Electronegativity: negative charge is more stable on more electronegative atoms (O more stable than N, which is more stable than C).
• Resonance: delocalizing charge increases stability (carboxylate is resonance-stabilized).
• Inductive effects: electron-withdrawing groups stabilize negative charge by pulling electron density.
• Hybridization: sp (more s-character) stabilizes negative charge better than sp² or sp³.

Typical acidity order to remember:

• Carboxylic acids are much more acidic than alcohols (resonance-stabilized carboxylate).
• Phenols are more acidic than aliphatic alcohols (resonance stabilization into the aromatic ring).
• Terminal alkynes are more acidic than alkenes/alkanes (hybridization effect).

For basicity, think about how available the lone pair is to accept a proton. Resonance can reduce basicity if it delocalizes
the lone pair (e.g., amide nitrogen is not very basic). Electron-donating groups increase basicity; electron-withdrawing groups
decrease it.

Reaction Types: The “Big Four” Patterns

Instead of memorizing many reactions, classify most NMAT organic reactions into a few patterns:

• Substitution: one group replaces another (common for alkyl halides).
• Elimination: removal of groups to form a pi bond (alkene formation).
• Addition: adding atoms across a pi bond (alkenes/alkynes).
• Oxidation/Reduction: change in oxidation state, often involving oxygen/hydrogen changes in organic molecules.

When faced with a question, first identify the functional group and choose the likely reaction class. Then decide whether the
conditions favor a particular pathway.

Nucleophiles and Electrophiles: Who Attacks Whom?

Nucleophiles donate electron pairs; electrophiles accept them. Common nucleophiles at NMAT level:

• OH⁻, OR⁻ (alkoxides)
• NH₃, amines
• CN⁻, HS⁻
• Halides (I⁻, Br⁻, Cl⁻) under appropriate conditions

Common electrophiles:

• Carbocations (in some mechanisms)
• Polarized carbonyl carbon (C=O)
• Alkyl carbon bearing a good leaving group (R–X, protonated alcohols)

A quick test: nucleophiles often have negative charge, lone pairs, or pi bonds; electrophiles often carry positive charge or
are attached to electronegative atoms that pull electron density away.

Substitution and Elimination: SN1, SN2, E1, E2 Essentials

Alkyl halides and related substrates (like protonated alcohols) commonly undergo substitution or elimination.
At NMAT level, you should know the basic differences:

SN2 (bimolecular nucleophilic substitution)

• One-step, backside attack, inversion of configuration if chiral center involved.
• Favored by strong nucleophiles and less hindered substrates (methyl > primary > secondary; tertiary is poor).
• Polar aprotic solvents (e.g., acetone, DMSO) often favor SN2.

SN1 (unimolecular nucleophilic substitution)

• Two-step: leaving group leaves first, forming a carbocation, then nucleophile attacks.
• Favored by substrates that form stable carbocations (tertiary > secondary; primary rarely).
• Leads to racemization at a chiral center due to planar carbocation intermediate.
• Polar protic solvents (e.g., water, alcohols) often favor SN1.

E2 (bimolecular elimination)

• One-step elimination to form an alkene; requires a strong base.
• Often competes with SN2; bulky bases tend to favor elimination.
• Anti-periplanar geometry is important (especially in cyclic systems).

E1 (unimolecular elimination)

• Two-step via carbocation like SN1, but results in alkene formation.
• Often occurs with weak bases under conditions that stabilize carbocations.

A highly testable concept is carbocation stability: tertiary > secondary > primary > methyl.
Resonance stabilization (allylic/benzylic carbocations) also increases stability.

Addition Reactions of Alkenes: Markovnikov vs Anti-Markovnikov

Alkenes react because the pi bond is electron-rich and can be attacked by electrophiles. Addition reactions typically break the
pi bond and form two new sigma bonds. A common NMAT focus is regioselectivity.

Markovnikov’s rule (in many additions): when adding HX to an unsymmetrical alkene, the H goes to the carbon with more
hydrogens (less substituted), and X goes to the more substituted carbon. This trend is often explained by formation of the more
stable carbocation intermediate.

Some conditions can give anti-Markovnikov outcomes (not always heavily tested), but if the question hints at “peroxide effect”
or radical conditions, it may reverse the addition pattern for HBr in particular.

Also remember that addition can affect stereochemistry: some reagents add in a specific way (syn vs anti), but NMAT typically
tests the bigger picture: recognizing that the double bond becomes single bond and two atoms/groups add across it.

Carbonyl Chemistry: Why C=O Is Special

The carbonyl group (C=O) is one of the most important functional groups. Oxygen is more electronegative than carbon, so the bond is
polar: the carbonyl carbon is electrophilic, and oxygen is nucleophilic/basic. This polarity drives many reactions.

At NMAT level, expect conceptual questions like:

• Which carbon in a molecule is most electrophilic?
• Which functional group undergoes nucleophilic addition vs substitution?
• Which compound is more reactive: aldehyde or ketone?

Aldehydes are generally more reactive than ketones toward nucleophilic addition because aldehydes are less sterically hindered
and have fewer electron-donating alkyl groups.

Carboxylic Acids and Derivatives: Relative Reactivity

Carboxylic acid derivatives include acid chlorides, anhydrides, esters, and amides. Their reactivity toward nucleophilic acyl
substitution depends largely on the leaving group ability. A common simplified order:

• Acid chloride (most reactive)
• Anhydride
• Ester
• Amide (least reactive)

Amides are less reactive because the nitrogen donates electron density by resonance, stabilizing the carbonyl and making the
C=O carbon less electrophilic. This same resonance is why amide nitrogen is much less basic than typical amines.

Oxidation and Reduction: Practical NMAT Patterns

NMAT questions may test oxidation states in organic molecules using simplified rules:

• Oxidation often means more bonds to oxygen or fewer bonds to hydrogen.
• Reduction often means more bonds to hydrogen or fewer bonds to oxygen.

Common transformations to recognize:

• Primary alcohol → aldehyde → carboxylic acid (increasing oxidation)
• Secondary alcohol → ketone (oxidation)
• Carbonyl (aldehyde/ketone) → alcohol (reduction)

Even if specific reagents are not emphasized, understanding the direction of change can help answer questions about products and
which compound is more oxidized.

Aromaticity and Benzene: Stability Through Resonance

Aromatic compounds (like benzene) are unusually stable due to delocalized pi electrons. Benzene is planar with a ring of
conjugated pi bonds, leading to resonance stabilization. Because aromaticity is stabilizing, benzene tends to undergo
reactions that preserve the aromatic ring.

Therefore, benzene commonly undergoes electrophilic aromatic substitution rather than addition (which would break aromaticity).
At NMAT level, you may be asked to identify aromatic vs non-aromatic structures, or to recognize that substitution is typical.

Common NMAT Skills: Stability Rankings and “Best Explanation” Questions

A frequent NMAT style is: “Which is more stable?” or “Which intermediate forms more easily?” Practice these ranking concepts:

• Carbocation stability: tertiary > secondary > primary > methyl; allylic/benzylic are resonance-stabilized.
• Radical stability (often similar trend): tertiary > secondary > primary > methyl; allylic/benzylic stabilized by resonance.
• Carbanion stability (often opposite trend unless resonance/inductive factors apply): methyl > primary > secondary > tertiary in simple alkyl cases, but stabilized strongly by electron-withdrawing groups and resonance.
• Leaving group ability: generally better leaving groups are weak bases (I⁻ > Br⁻ > Cl⁻ > F⁻), and sulfonates are excellent (if included).
• Acidity: more stable conjugate base means stronger acid (resonance and electronegativity matter a lot).

When asked “why,” choose explanations based on resonance stabilization, inductive effects, and steric hindrance.
Those are the most “testable reasons.”

Study Strategy for NMAT Organic Chemistry

To study efficiently:

• Master functional group recognition: you should identify a functional group in under 3 seconds.
• Practice ranking problems: acidity/basicity, stability, boiling points, and reactivity orders.
• Learn the reaction patterns: substitution vs elimination; addition across alkenes; nucleophilic attack on carbonyls.
• Use “electron-rich vs electron-poor” thinking instead of memorizing full mechanisms.
• Do timed drills: NMAT rewards speed plus accuracy; train quick elimination of wrong choices.

If you consistently ask: “Where are the electrons? Where are they going?” you’ll solve many questions without needing a long mechanism.
Organic chemistry becomes a logic puzzle, and the NMAT tends to reward that logic.

Quick Summary: Must-Know Takeaways

• Recognize common functional groups and interpret skeletal structures quickly.
• Hybridization affects geometry and acidity: sp > sp² > sp³ acidity for C–H bonds.
• Acidity depends on conjugate base stability (resonance, inductive effects, electronegativity).
• Substitution and elimination depend on substrate type, nucleophile/base strength, and sterics (SN1/SN2/E1/E2 patterns).
• Alkenes undergo addition; Markovnikov pattern is common when carbocation stability matters.
• Carbonyl carbon is electrophilic; aldehydes are generally more reactive than ketones.
• Aromaticity creates stability; benzene prefers substitution to preserve aromaticity.

With these fundamentals, you’ll be ready for the majority of NMAT organic chemistry questions that focus on conceptual understanding and trend-based reasoning.

Organic Chemistry Fundamentals: Problem Sets

Question Set 1: Structures, Functional Groups, and Nomenclature

1. Which functional group is present in CH3CH2OH?
2. Which compound is an aldehyde?
   1. CH3COCH3
   2. CH3CHO
   3. CH3COOH
   4. CH3OCH3
3. How many carbon atoms are implied in a skeletal (line-angle) structure that shows a straight chain with 5 vertices (including endpoints) and no heteroatoms?
4. Which pair represents constitutional isomers?
   1. cis-2-butene and trans-2-butene
   2. ethanol and dimethyl ether
   3. (R)-2-butanol and (S)-2-butanol
   4. benzene and cyclohexane
5. Identify the functional group in CH3COOCH2CH3.
6. Which compound is most likely aromatic?
   1. cyclohexane
   2. benzene
   3. cyclohexene
   4. cyclopentane

Question Set 2: Bonding, Hybridization, and Geometry

1. What is the hybridization of carbon in CH4?
2. What is the hybridization of each carbon in ethene (C2H4)?
3. What is the approximate bond angle around an sp2-hybridized carbon?
4. Which carbon is sp-hybridized?
   1. carbon in CH3CH3
   2. carbon in CH2=CH2
   3. terminal carbon in HC≡CH
   4. carbonyl carbon in CH3CHO
5. Rank the following C–H acids from most acidic to least acidic: alkane (sp3 C–H), alkene (sp2 C–H), terminal alkyne (sp C–H).

Question Set 3: Polarity, Intermolecular Forces, and Physical Properties

1. Which has the highest boiling point (similar molar masses assumed)?
   1. propane (C3H8)
   2. dimethyl ether (CH3OCH3)
   3. 1-propanol (CH3CH2CH2OH)
   4. propene (C3H6)
2. Which intermolecular force is primarily responsible for the unusually high boiling point of alcohols compared with alkanes?
3. Which compound is most soluble in water?
   1. hexane
   2. 1-hexanol
   3. ethanol
   4. benzene
4. “Like dissolves like” means:
5. Between ethane and butane, which has the higher boiling point and why (one main reason)?

Question Set 4: Acidity and Basicity

1. Which is the strongest acid?
   1. ethanol (CH3CH2OH)
   2. acetic acid (CH3COOH)
   3. ammonia (NH3)
   4. propane (C3H8)
2. Which conjugate base is most resonance-stabilized?
   1. ethoxide (CH3CH2O−)
   2. acetate (CH3COO−)
   3. amide anion (NH2−)
   4. methyl anion (CH3−)
3. Which is more basic: an amide nitrogen or an amine nitrogen?
4. Rank acidity (most acidic to least acidic): phenol, ethanol, acetic acid.
5. Which factor generally increases acidity the most?
   1. electron-donating groups near the acidic proton
   2. resonance stabilization of the conjugate base
   3. increasing alkyl substitution near the acidic proton
   4. decreasing electronegativity of the atom bearing negative charge in the conjugate base

Question Set 5: Nucleophiles, Electrophiles, and Reaction Patterns

1. Which is the best nucleophile in a typical polar aprotic solvent?
   1. H2O
   2. OH−
   3. CH3OH
   4. NH4+
2. In a carbonyl group (C=O), which atom is more electrophilic?
3. Classify the reaction type: converting an alkyl halide (R–Br) to an alcohol (R–OH) using OH−.
4. Classify the reaction type: converting an alkyl halide (R–Br) to an alkene using a strong base.
5. Which is a better leaving group?
   1. F−
   2. Cl−
   3. Br−
   4. I−

Question Set 6: Substitution and Elimination (SN1/SN2/E1/E2)

1. Which substrate is most likely to undergo SN1?
   1. CH3Br
   2. CH3CH2Br
   3. (CH3)3CBr
   4. CH2=CHCH2Br
2. Which substrate is best suited for SN2?
   1. (CH3)3CBr
   2. CH3Br
   3. secondary alkyl bromide (R2CHBr)
   4. tert-butyl chloride with water
3. A chiral center undergoing SN2 will most directly result in:
4. A chiral center undergoing SN1 will most directly result in:
5. Bulky strong bases tend to favor which pathway when reacting with secondary alkyl halides?
   1. SN2
   2. SN1
   3. E2
   4. addition

Question Set 7: Alkene Addition and Regioselectivity

1. When HBr adds to propene (CH3–CH=CH2) under typical ionic conditions, the major product is:
   1. 1-bromopropane
   2. 2-bromopropane
   3. 3-bromopropane
   4. propyl alcohol
2. Markovnikov’s rule predicts that in HX addition to an unsymmetrical alkene, X attaches to the:
3. What key intermediate often explains Markovnikov orientation in ionic additions?
4. What happens to the pi bond during an addition reaction?
5. Which alkene is expected to form a more stable carbocation intermediate upon protonation?
   1. ethene
   2. propene
   3. 2-methylpropene
   4. 1-butene

Question Set 8: Carbonyls and Carboxylic Acid Derivatives

1. Which is generally more reactive toward nucleophilic addition?
   1. aldehyde
   2. ketone
   3. amide
   4. ether
2. In nucleophilic attack on a carbonyl, the nucleophile attacks the:
3. Rank these carboxylic acid derivatives from most reactive to least reactive: acid chloride, ester, amide, anhydride.
4. Which derivative is least reactive and why (one key reason)?
5. Which compound is a carboxylic acid?
   1. CH3COCH3
   2. CH3COOH
   3. CH3CHO
   4. CH3COOCH3

Organic Chemistry Fundamentals: Answer Keys

Answer Key Set 1

1. Alcohol (hydroxyl group)
2. B
3. 5 carbon atoms
4. B
5. Ester
6. B

Answer Key Set 2

1. sp3
2. sp2 for both carbons
3. Approximately 120°
4. C
5. terminal alkyne (sp) > alkene (sp2) > alkane (sp3)

Answer Key Set 3

1. C
2. Hydrogen bonding
3. C
4. Polar substances dissolve best in polar solvents, and nonpolar substances dissolve best in nonpolar solvents.
5. Butane, because it has greater London dispersion forces due to larger size/surface area.

Answer Key Set 4

1. B
2. B
3. Amine nitrogen is more basic than amide nitrogen.
4. acetic acid > phenol > ethanol
5. B

Answer Key Set 5

1. B
2. Carbon (the carbonyl carbon)
3. Substitution (nucleophilic substitution)
4. Elimination (to form an alkene)
5. D

Answer Key Set 6

1. C
2. B
3. Inversion of configuration (backside attack)
4. Racemization (mixture of configurations due to planar carbocation)
5. C

Answer Key Set 7

1. B
2. More substituted carbon (the carbon with fewer hydrogens)
3. A carbocation intermediate
4. The pi bond breaks and is replaced by two new sigma bonds.
5. C

Answer Key Set 8

1. A
2. Carbonyl carbon
3. acid chloride > anhydride > ester > amide
4. Amide, because resonance donation from nitrogen reduces electrophilicity and makes leaving group departure difficult.
5. B

NMAT Chemistry Review: NMAT Study Guide