The Thorpe–Ingold effect, gem-dimethyl effect, or angle compression is an effect observed in chemistry where large substituents favor ring closure and intramolecular reactions. The effect was first reported by Beesley, Thorpe, and Ingold in 1915 as part of a study of cyclization reactions.It has since been generalized to many areas of chemistry.
The comparative rates of lactone formation (lactonization) of various 2-hydroxybenzenepropionic acids illustrate the effect. The placement of an increasing number of methyl groups accelerates the cyclization process.
One application of this effect is addition of a quaternary carbon (e.g., a gem-dimethyl group) in an alkyl chain to increase the reaction rate and/or equilibrium constant of cyclization reactions. An example of this is an olefin metathesis reaction:In the field of peptide foldamers, amino acid residues containing quaternary carbons such as 2-Aminoisobutyric acid are used to promote formation of certain types of helices.
One proposed explanation for this effect is that the increased size of the substituents increases the angle between them. As a result, the angle between the other two substituents decreases. By moving them closer together, reactions between them are accelerated. It is thus a kinetic effect.
The effect also has some thermodynamic contribution as the in silico strain energy decreases on going from cyclobutane to 1-methylcyclobutane and 1,1-dimethylcyclobutane by a value between 8 kcal/moleand 1.5 kcal/mole. A noteworthy example of the Thorpe-Ingold effect in supramolecular catalysis is given by diphenylmethane derivatives provided with guanidinium groups. These compounds are active in the cleavage of the RNA model compound HPNP. Substitution of the methylene group of the parent diphenylmethane spacer with cyclohexylidene and adamantylidene moieties enhances catalytic efficiency, with gem dialkyl effect accelerations of 4.5 and 9.1, respectively.
Allenes are organic compounds in which one carbon atom has double bonds with each of its two adjacent carbon centres. Allenes are classified as cumulated dienes. The parent compound of this class is propadiene, which is itself also called allene. Compounds with an allene-type structure but with more than three carbon atoms are members of a larger class of compounds called cumulenes with X=C=Y bonding.
Intramolecular in chemistry describes a process or characteristic limited within the structure of a single molecule, a property or phenomenon limited to the extent of a single molecule.
A carbanion is an anion in which carbon is trivalent and bears a formal negative charge.
In chemistry, a carbene is a molecule containing a neutral carbon atom with a valence of two and two unshared valence electrons. The general formula is R-(C:)-R' or R=C: where the R represent substituents or hydrogen atoms.
Steric effects are nonbonding interactions that influence the shape (conformation) and reactivity of ions and molecules. Steric effects complement electronic effects, which dictate the shape and reactivity of molecules. Steric repulsive forces between overlapping electron clouds result in structured groupings of molecules stabilized by the way that opposites attract and like charges repel.
In chemistry, a molecule experiences strain when its chemical structure undergoes some stress which raises its internal energy in comparison to a strain-free reference compound. The internal energy of a molecule consists of all the energy stored within it. A strained molecule has an additional amount of internal energy which an unstrained molecule does not. This extra internal energy, or strain energy, can be likened to a compressed spring. Much like a compressed spring must be held in place to prevent release of its potential energy, a molecule can be held in an energetically unfavorable conformation by the bonds within that molecule. Without the bonds holding the conformation in place, the strain energy would be released.
A 1,2-rearrangement or 1,2-migration or 1,2-shift or Whitmore 1,2-shift is an organic reaction where a substituent moves from one atom to another atom in a chemical compound. In a 1,2 shift the movement involves two adjacent atoms but moves over larger distances are possible. In the example below the substituent R moves from carbon atom C2 to C3.
A transition metal carbene complex is an organometallic compound featuring a divalent organic ligand. The divalent organic ligand coordinated to the metal center is called a carbene. Carbene complexes for almost all transition metals have been reported. Many methods for synthesizing them and reactions utilizing them have been reported. The term carbene ligand is a formalism since many are not derived from carbenes and almost none exhibit the reactivity characteristic of carbenes. Described often as M=CR2, they represent a class of organic ligands intermediate between alkyls (−CR3) and carbynes (≡CR). They feature in some catalytic reactions, especially alkene metathesis, and are of value in the preparation of some fine chemicals.
Pentane interference or syn-pentane interaction is the steric hindrance that the two terminal methyl groups experience in one of the chemical conformations of n-pentane. The possible conformations are combinations of anti conformations and gauche conformations and are anti-anti, anti-gauche+, gauche+ - gauche+ and gauche+ - gauche− of which the last one is especially energetically unfavorable. In macromolecules such as polyethylene pentane interference occurs between every fifth carbon atom. The 1,3-diaxial interactions of cyclohexane derivatives is a special case of this type of interaction, although there are additional gauche interactions shared between substituents and the ring in that case. A clear example of the syn-pentane interaction is apparent in the diaxial versus diequatorial heats of formation of cis 1,3-dialkyl cyclohexanes. Relative to the diequatorial conformer, the diaxial conformer is 2-3 kcal/mol higher in energy than the value that would be expected based on gauche interactions alone. Pentane interference helps explain molecular geometries in many chemical compounds, product ratios, and purported transition states. One specific type of syn-pentane interaction is known as 1,3 allylic strain or.
In organic chemistry, helicenes are ortho-condensed polycyclic aromatic compounds in which benzene rings or other aromatics are angularly annulated to give helically-shaped chiral molecules. The chemistry of helicenes has attracted continuing attention because of their unique structural, spectral, and optical features.
In organic chemistry, transannular strain is the unfavorable interactions of ring substituents on non-adjacent carbons. These interactions, called transannular interactions, arise from a lack of space in the interior of the ring, which forces substituents into conflict with one another. In medium-sized cycloalkanes, which have between 8 and 11 carbons constituting the ring, transannular strain can be a major source of the overall strain, especially in some conformations, to which there is also contribution from large-angle strain and Pitzer strain. In larger rings, transannular strain drops off until the ring is sufficiently large that it can adopt conformations devoid of any negative interactions.
Ring-closing metathesis (RCM) is a widely used variation of olefin metathesis in organic chemistry for the synthesis of various unsaturated rings via the intramolecular metathesis of two terminal alkenes, which forms the cycloalkene as the E- or Z- isomers and volatile ethylene.
The Peterson olefination is the chemical reaction of α-silyl carbanions with ketones to form a β-hydroxysilane (2) which eliminates to form alkenes (3).
The Combes quinoline synthesis is a chemical reaction, which was first reported by Combes in 1888. It involves the condensation of unsubstituted anilines (1) with β-diketones (2) to form substituted quinolines (4) after an acid-catalyzed ring closure of an intermediate Schiff base (3). Further studies and reviews of the Combes quinoline synthesis and its variations have been published by Alyamkina et al., Bergstrom and Franklin, Born, and Johnson and Mathews.
Allylic strain in organic chemistry is a type of strain energy resulting from the interaction between a substituent on one end of an olefin with an allylic substituent on the other end. If the substituents are large enough in size, they can sterically interfere with each other such that one conformer is greatly favored over the other. Allyic strain was first recognized in the literature in 1965 by Johnson and Malhotra. The authors were investigating cyclohexane conformations including endocyclic and exocylic double bonds when they noticed certain conformations were disfavored due to the geometry constraints caused by the double bond. Organic chemists capitalize on the rigidity resulting from allylic strain for use in asymmetric reactions.
In organometallic chemistry, a metallacycle is a derivative of a carbocyclic compound wherein a metal has replaced at least one carbon center; this is to some extent similar to heterocycles. Metallacycles appear frequently as reactive intermediates in catalysis, e.g. olefin metathesis and alkyne trimerization. In organic synthesis, directed ortho metalation is widely used for the functionalization of arene rings via C-H activation. One main effect that metallic atom substitution on a cyclic carbon compound is distorting the geometry due to the large size of typical metals.
Sir Jocelyn Field Thorpe FRS  was a British chemist who made major contributions to organic chemistry., including the Thorpe-Ingold effect and three named reactions.
In chemistry, solvent effects are the influence of a solvent on chemical reactivity or molecular associations. Solvents can have an effect on solubility, stability and reaction rates and choosing the appropriate solvent allows for thermodynamic and kinetic control over a chemical reaction.
The Birch reduction is an organic reaction that is used to convert arenes to cyclohexadienes. The reaction is named after the Australian chemist Arthur Birch. In this organic reduction of aromatic rings in liquid ammonia with sodium, lithium, or potassium and an alcohol, such as ethanol and tert-butanol. This reaction is unlike catalytic hydrogenation, which usually reduces the aromatic ring all the way to a cyclohexane.
Trifluoronitrosomethane is a toxic organic compound consisting of a trifluoromethyl group covalently bound to a nitroso group. Its distinctive deep blue color is unusual for a gas.