Difficulty: Beginner–Intermediate | Prerequisites: Lewis structures, basic bonding, periodic table trends.
This set of notes covers the grab-bag of foundational topics that come up alongside stereochemistry and conformational analysis in Organic Chemistry II: how to name compounds properly, how to describe the electron geometry around atoms, how resonance stabilises ions and molecules, what makes one acid stronger than another, and the basic reaction types you need to classify. These topics thread through every subsequent chapter, so gaps here compound quickly.
IUPAC naming follows a systematic set of rules based on the longest chain, substituent positions and functional group suffixes. Hybridisation (sp, sp2, sp3) determines molecular geometry. Resonance delocalisation lowers energy and stabilises ions. Lower pKa means stronger acid; electron-withdrawing groups increase acidity. Alcohols are hydrogen bond donors; ketones and ethers are only acceptors. Converting an acid chloride to an ester with an alcohol is nucleophilic acyl substitution. The first principle of green chemistry is preventing waste.
IUPAC nomenclature
The systematic method for naming organic compounds, governed by the International Union of Pure and Applied Chemistry. Names are built from the longest carbon chain (parent), substituent prefixes and a functional group suffix.
Hybridisation
The mixing of atomic orbitals to form new hybrid orbitals. sp3 = 4 electron domains, tetrahedral (109.5°). sp2 = 3 electron domains, trigonal planar (120°). sp = 2 electron domains, linear (180°).
Think of it as: count the electron domains (bonds + lone pairs) around the atom, then the hybridisation follows.
Resonance
The delocalisation of electrons (typically pi electrons or lone pairs) across multiple atoms, represented by two or more Lewis structures (resonance contributors). The true structure is a hybrid, lower in energy than any single contributor.
pKa
The negative log of the acid dissociation constant. Lower pKa = stronger acid. A difference of one pKa unit means a tenfold difference in acid strength.
Inductive effect
The electron-withdrawing or electron-donating effect transmitted through sigma bonds. Electronegative atoms (F, Cl, O) withdraw electron density, stabilising nearby negative charges and increasing acidity.
Hydrogen bond donor
A functional group with a hydrogen covalently bonded to a highly electronegative atom (N, O, F). Alcohols (R-OH) and amines (R-NH2) are donors. Ketones and ethers are acceptors only.
Nucleophilic acyl substitution
A reaction in which a nucleophile attacks a carbonyl carbon, forming a tetrahedral intermediate, and a leaving group departs. Classic example: alcohol + acid chloride → ester + HCl.
Green chemistry
A set of 12 principles for designing chemical processes that reduce or eliminate hazardous substances. The first and overarching principle is waste prevention.
Find the longest continuous carbon chain that includes the principal functional group. This gives the parent name (methane, ethane, propane, butane, pentane...).
Number the chain from the end that gives the functional group the lowest locant.
Name substituents as prefixes (methyl, ethyl, chloro, bromo...) with their position numbers.
The functional group determines the suffix: -ol (alcohol), -al (aldehyde), -one (ketone), -oic acid (carboxylic acid), -amine (amine).
Worked example: (CH3)2CHCH2Cl. The longest chain is 3 carbons (propane). Chlorine is on C1, methyl branch on C2. Name: 1-chloro-2-methylpropane.
Worked example: CH3CH(CH3)CH2CH2OH. The longest chain containing -OH is 4 carbons (butanol). Number from the -OH end: OH at C1, methyl at C3. Name: 3-methyl-1-butanol.
Alcohol: -ol
Aldehyde: -al
Ketone: -one
Carboxylic acid: -oic acid
Ester: -oate
Amine: -amine
The hybridisation of an atom is determined by its number of electron domains (bonds + lone pairs, where a double or triple bond counts as one domain).
sp3: 4 electron domains. Tetrahedral geometry, ~109.5° bond angles. Example: nitrogen in a primary amine (R-NH2) has three bonds + one lone pair = 4 domains = sp3.
sp2: 3 electron domains. Trigonal planar geometry, ~120° bond angles. Example: the carbonyl carbon in formaldehyde (CH2O) has two C-H bonds + one C=O bond = 3 domains = sp2. One unhybridised p-orbital forms the pi bond.
sp: 2 electron domains. Linear geometry, 180° bond angles. Example: the carbon in acetylene (C2H2).
Resonance occurs when electrons (usually pi electrons or lone pairs) can be delocalised across multiple atoms. The molecule is not "flipping" between structures; the true structure is a weighted average (the resonance hybrid).
Resonance stabilisation: the hybrid is lower in energy than any individual contributor. More delocalisation = more stabilisation.
Acetate ion (CH3COO-): two equivalent resonance structures, with the negative charge on either oxygen. Because both structures are identical in form, they contribute equally, and each C-O bond is identical (bond order 1.5).
Nitrate ion (NO3-): three equivalent resonance structures, with the double bond on each of the three oxygens in turn. The charge is spread over all three oxygens, making the ion unusually stable. Equal N-O bond lengths in the hybrid confirm the delocalisation.
Aniline (PhNH2): the nitrogen lone pair is delocalised into the aromatic ring via resonance. This is why aniline is a weaker base than cyclohexylamine: the lone pair is partially tied up in the pi system.
Lower pKa = stronger acid = more readily donates a proton.
Ranking (most acidic first): HCl (pKa ~ -7) > CF3CO2H (pKa 0.23) > CH3CO2H (pKa 4.76) > H2O (pKa 15.7).
The fluorine atoms in trifluoroacetic acid withdraw electron density through the inductive effect, stabilising the conjugate base (the carboxylate anion) and making the acid much stronger than acetic acid.
A hydrogen bond donor requires an H bonded to N, O, or F. Alcohols (R-OH) and amines (R-NH2) are donors. Ketones (C=O) and ethers (R-O-R) have lone pairs on oxygen and can accept hydrogen bonds, but they have no O-H or N-H bond, so they cannot donate.
Nucleophilic acyl substitution: a nucleophile attacks a carbonyl carbon bearing a leaving group. The leaving group departs. Converting an acid chloride to an ester using an alcohol is the classic example: the alcohol is the nucleophile, chloride is the leaving group.
The 12 principles of green chemistry provide a hierarchy for designing cleaner chemical processes. The first principle, and the one most frequently tested, is waste prevention: it is better to prevent waste from being generated than to treat or clean it up after the fact.
Confusing common names with IUPAC names. "Isobutyl chloride" is a common name, not IUPAC. The correct IUPAC name for (CH3)2CHCH2Cl is 1-chloro-2-methylpropane.
Students often think that a ketone (C=O) can donate hydrogen bonds. It cannot, because there is no O-H or N-H bond. It can only accept.
Assuming resonance structures are real, separate molecules that interconvert. They are not. The molecule exists as one hybrid; the resonance structures are a bookkeeping tool.
Thinking higher pKa = stronger acid. The relationship is inverted: lower pKa = stronger acid.
⚠️ IUPAC naming is tested directly. Know the suffixes (-ol, -al, -one, -oic acid) and the rules for finding the longest chain and numbering it correctly.
⚠️ Hybridisation questions ask you to identify the hybridisation of a specific atom. Count electron domains, not just bonds.
⚠️ Resonance stability questions (nitrate ion, acetate ion) want you to explain why delocalisation lowers energy and how equivalent contributors make a molecule especially stable.
⚠️ Acidity rankings are a favourite exam format. Memorise representative pKa values and understand how inductive effects and resonance stabilisation of the conjugate base affect acidity.
⚠️ The first principle of green chemistry (waste prevention) is the most commonly tested of the twelve.
The IUPAC suffix for a carboxylic acid is ____. (-oic acid.)
The carbonyl carbon in formaldehyde is ____ hybridised. (sp2.)
True or false: the nitrogen lone pair in aniline is not involved in resonance. (False. It is delocalised into the ring.)
Which is more acidic: CH3CO2H or CF3CO2H? (CF3CO2H. Lower pKa.)
True or false: ethers can donate hydrogen bonds. (False. They can only accept.)
Q: What is the IUPAC name for (CH3)2CHCH2Cl?
A: 1-chloro-2-methylpropane. The longest chain is propane (3 carbons). Cl is on C1, methyl on C2.
Q: Give the IUPAC name for CH3CH(CH3)CH2CH2OH.
A: 3-methyl-1-butanol. The parent chain is butanol (4 carbons with -OH). Number from the -OH end: OH at C1, methyl at C3.
Q: Describe the hybridisation and geometry of the carbonyl carbon in formaldehyde.
A: The carbonyl carbon has three electron domains (two C-H bonds and one C=O double bond). It is sp2 hybridised with trigonal planar geometry and ~120° bond angles. One unhybridised p-orbital participates in the pi bond with oxygen.
Q: Draw the two resonance contributors of the acetate ion and state whether they are equivalent.
A: In one contributor, one oxygen bears the double bond and the other carries the negative charge. In the second, the roles are reversed. The two structures are equivalent because both oxygens are identical (same element, same bonding environment). They contribute equally to the hybrid.
Q: Rank HCl, H2O, CH3CO2H and CF3CO2H in order of increasing acidity (lowest to highest pKa).
A: HCl (pKa ~ -7) < CF3CO2H (0.23) < CH3CO2H (4.76) < H2O (15.7). Lowest pKa = most acidic = listed first.
Q: What type of reaction is the conversion of an acid chloride to an ester using an alcohol?
A: Nucleophilic acyl substitution. The alcohol (nucleophile) attacks the carbonyl carbon, and chloride (leaving group) departs.
Q: What is the first principle of green chemistry?
A: Preventing waste. It is better to prevent waste at the source than to treat or clean it up afterwards.
Q: Which atom in aniline has its lone pair involved in resonance delocalisation?
A: Nitrogen. Its lone pair delocalises into the aromatic ring via resonance, which is why aniline is a weaker base than a typical aliphatic amine.
IUPAC nomenclature is used in every subsequent chapter to describe reagents, products and intermediates. Hybridisation determines reactivity: sp2 carbons are electrophilic in carbonyl chemistry, while sp3 carbons are the targets in substitution and elimination reactions. Resonance stabilisation explains why carboxylate anions are weaker bases than alkoxide ions, which feeds directly into acidity comparisons and nucleophilicity rankings.
IUPAC nomenclature, naming organic compounds, longest chain rule, functional group suffix, -ol, -al, -one, -oic acid, hybridisation, sp3, sp2, sp, trigonal planar, tetrahedral, resonance structures, resonance hybrid, delocalisation, resonance stabilisation, acetate ion resonance, nitrate ion resonance, pKa, acidity ranking, inductive effect, electron-withdrawing group, trifluoroacetic acid, hydrogen bond donor, hydrogen bond acceptor, alcohol, ketone, ether, nucleophilic acyl substitution, acid chloride to ester, green chemistry, waste prevention, 12 principles of green chemistry, aniline resonance, CH 2420, University of Michigan organic chemistry