Physical organic chemistry

right|thumb|Two different Resonance (chemistry)|resonance forms of benzene (top) combine to produce an average structure (bottom) In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected from conjugation alone. The earliest use of the term was in an article by August Wilhelm Hofmann in 1855. There is no general relationship between aromaticity as a chemical property and the olfactory properties of such compounds.

empirical rule for predicting the outcome of some addition reactions

thumb|A hydroxide ion acting as a nucleophile in an SN2 reaction, converting a [[haloalkane into an alcohol]] In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are Lewis bases.

In chemistry, an electrophile is a chemical species that forms bonds with nucleophiles by accepting an electron pair. Because electrophiles accept electrons, they are Lewis acids. Most electrophiles are positively charged, have an atom that carries a partial positive charge, or have an atom that does not have an octet of electrons.

thumb|300px|Rotation about single bond of butane to interconvert one conformation to another. The gauche conformation on the right is a conformer, while the eclipsed conformation on the left is a transition state between conformers. Above: Newman projection; below: depiction of spatial orientation.

system of connected p orbitals with delocalized electrons increasing molecular stability

geometric aspects of ions and molecules affecting their shape and reactivity

empirical rule predicting the major product(s) in elimination reaction

local change in the electron density of a molecule due to electron-withdrawing or electron-donating groups elsewhere in the molecule, resulting in a permanent dipole in a bond

method of determining aromaticity in organic molecules

In organic chemistry, hyperconjugation (σ-conjugation or no-bond resonance) refers to the delocalization of electrons with the participation of bonds of primarily σ-character. Usually, hyperconjugation involves the interaction of the electrons in a sigma (σ) orbital (e.g. C–H or C–C) with an adjacent unpopulated non-bonding p or antibonding σ* or π* orbitals to give a pair of extended molecular orbitals. However, sometimes, low-lying antibonding σ* orbitals may also interact with filled orbitals of lone pair character (n) in what is termed negative hyperconjugation. Increased electron delocali

set of rules used to rationalize or predict certain aspects of the stereochemistry and activation energy of pericyclic reactions

discipline of organic chemistry

instability in molecules with bonds at unnatural angles

measure of acidity used for extremely acidic solutions

thumb|upright=1.4|Structure and [[Atomic force microscopy|AFM image of a hexadehydrotribenzo[12]annulene]] Annulenes are monocyclic hydrocarbons that contain the maximum number of non-cumulated or conjugated double bonds ('mancude'), and their derivatives. They have the general formula CnHn (when n is an even number) or CnHn+1 (when n is an odd number). The IUPAC accepts the use of 'annulene nomenclature' in naming carbocyclic ring systems with 7 or more carbon atoms, using the name '[n]annulene' for the mancude hydrocarbon with n carbon atoms in its ring, though in certain contexts (e.g., dis

Empirical observation that states that a double bond cannot be placed at the bridgehead of a bridged ring system

guidelines outlining the relative favorabilities of ring closure reactions in alicyclic compounds

Antiaromaticity is a chemical property of a cyclic molecule with a π electron system that has higher energy, i.e., it is less stable due to the presence of 4n delocalised (π or lone pair) electrons in it, as opposed to aromaticity. Unlike aromatic compounds, which follow Hückel's rule ([4n+2] π electrons) and are highly stable, antiaromatic compounds are highly unstable and highly reactive. To avoid the instability of antiaromaticity, molecules may change shape, becoming non-planar and therefore breaking some of the π interactions. In contrast to the diamagnetic ring current present in aromati

free-energy relationship in organic chemistry

explanation for the rates of electron transfer reactions

association of molecules in which an electronic charge is transferred

stereoelectronic effect, tendency of heteroatomic substituents adjacent to a heteroatom within a cyclohexane ring to prefer the axial orientation instead of the less hindered equatorial orientation that would be expected from steric considerations

American chemist (1921–2005)

rules to predict the maximum absorption wavelength of a compound in UV-Vis spectra

phenomenon in physical organic chemistry

organic Chemistry Mechanism

hypothesis in physical organic chemistry

Effect in chemistry

influence of substituents on the thermodynamics and kinetics of ring-closing reactions in organic chemistry

300px|thumb|Delocalization of negative charge in a generic carboxylate anion, derived from an organic carboxylic acid (cf. acetic acid), and the corresponding vinylogous carboxylate anion (the "vinylog/vinylogue" of the carboxylate anion), where a vinyl group now separates the charged oxygen from the [[carbonyl () group. The validity of the theoretical concept of vinylogy is supported by the pKa of such vinylogs, which approach that of the analogous carboxylic acid.]]

intramolecular interaction

effect observed in aromatic molecules

Homoaromaticity, in organic chemistry, refers to a special case of aromaticity in which conjugation is interrupted by a single sp3 hybridized carbon atom. Although this sp3 center disrupts the continuous overlap of p-orbitals, traditionally thought to be a requirement for aromaticity, considerable thermodynamic stability and many of the spectroscopic, magnetic, and chemical properties associated with aromatic compounds are still observed for such compounds. This formal discontinuity is apparently bridged by p-orbital overlap, maintaining a contiguous cycle of π electrons that is responsible fo

special type of aromaticity exists in a number of organic molecules

Diagrams in physical organic chemistry

Rule in organic chemistry

the trajectory of approach of a nucleophile to an electrophilic carbon

Principle in chemical kinetics

relationship in physical organic chemistry

Measurements of stable atom orientations

influence other than bonding or steric effects on a molecule's properties

Silicon Hyperconjugation