Integrated SequencePhysics Chemistry Organic Biology

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Module 9 in the Syllabus

Conjugated Species Mechanisms
Mechanisms and explanations from the Organic Mechanisms Pocketbook

Aromatic Compounds Mechanisms
Mechanisms and explanations from the Organic Mechanisms Pocketbook

Conjugated &#pi; Systems and Aromaticity Images
Image gallery for study with links to larger teaching JPEGs for classroom presentation

Question Drill for Conjugated π Systems and Aromaticity
Conceptual Vocabulary Self-Test

Basic Terms Crossword Puzzle

Basic Puzzle Solution

Conceptual Vocabulary
AromaticityAromaticity is a chemical property in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibit a stabilization stronger than would be expected by the stabilization of conjugation alone.
Conjugated systemA chemically conjugated system is a system of atoms covalently bonded with alternating single and multiple bonds in a molecule of an organic compound.
Delocalized electronDelocalized electrons are electrons in a molecule that are not associated with a single atom or to a covalent bond.
Pi bondPi bonds are covalent chemical bonds where two lobes of one involved electron orbital overlap two lobes of the other involved electron orbital. Only one of the orbital's nodal planes passes through both of the involved nuclei.
DieneDienes are hydrocarbons which contain two double bonds.
BenzeneBenzene is an organic aromatic chemical compound whose molecules contain six carbons and six hydrogens.
Hückel's ruleHückel's rule estimates whether a planar ring molecule will have aromatic properties. It was first expressed succinctly as the 4n+2 rule by von Doering in 1951.
Aromatic ring currentAn aromatic ring current is an effect observed in aromatic molecules if a magnetic field is directed perpendicular to the plane of the aromatic system.
Heterocyclic compoundHeterocyclic compounds are organic compounds that contain a ring structure containing atoms in addition to carbon, such as sulfur, oxygen or nitrogen, as part of the ring.
PigmentOften compounds with extended conjugated systems, a pigment is a material that changes the color of light it reflects as the result of selective color absorption.
StackingStacking in supramolecular chemistry refers to a stacked arrangement of aromatic molecules, which interact through aromatic interactions.
ArylIn the context of organic molecules, aryl refers to any functional group or substituent derived from a simple aromatic ring.
CoplanarA set of points in space is coplanar if the points all lie in the same geometric plane.
NaphthaleneNaphthalene is a crystalline, aromatic, white, solid hydrocarbon, best known as the primary ingredient of mothballs.
PolyenePolyenes are poly-unsaturated organic compounds that contain one or more sequences of alternating double and single carbon-carbon bonds.
Polycyclic aromatic hydrocarbonPolycyclic aromatic hydrocarbons are chemical compounds that consist of fused aromatic rings and do not contain heteroatoms or carry substituents.
Cross-conjugationCross-conjugation is a special type of conjugation in a molecule, when in a set of three pi bonds only two pi-bonds interact with each other by conjugation, the third one is excluded from interaction.
TolueneToluene, also known as methylbenzene or phenylmethane, is a clear, water-insoluble liquid with the typical smell of paint thinners.
XyleneXylene refers to a group of 3 benzene derivatives which encompasses ortho-, meta-, and para- isomers of dimethyl benzene.
Advanced terms that may appear in context in MCAT passages
Hückel} methodThe Hückel method is a very simple LCAO MO Method for the determination of energies of molecular orbitals of pi electrons in conjugated hydrocarbon systems, such as ethene, benzene and butadiene.
HomoaromaticityHomoaromaticity in organic chemistry is found in conjugated cyclic systems that are able to skip a part of the ring as opposed to regular aromaticity.
CyclobutadieneCyclobutadiene is the smallest [n]-annulene, an extremely unstable hydrocarbon, failing Hückel's rule, because its ring has 4 pi-electrons, and 4 is not twice an odd number.
AntiaromaticAntiaromatic or pseudoaromatic molecules are cyclic systems containing alternating single and double bonds, where the pi electron energy of antiaromatic compounds is higher than that of its open-chain counterpart.
PAH world hypothesisThe PAH world hypothesis is a biological hypothesis that proposes that polycyclic aromatic hydrocarbons provided a means for a pre-RNA World basis for the origin of life.

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