Antiperiplanar: Definition, E2 Mechanism, Etymology And Historiography, FAQs

Anti-periplanar or Anti-periplanar refers to the A-B-C-D bond angles of a molecule in organic chemistry. The molecule becomes asymmetric at the Neumann ridge, with antiparallel functional groups facing up and down 180 degrees apart. Hyperconjugation occurs when parallel orbitals collide and become entangled.

Anti-periplanar is the same as Syn-periplanar or synperiplanar. In syn-periplanar conformers, A and D are on the same side of the bond plane, and the dihedral angles AB and C-D are between +30 and -30 degrees.

Definition Of Anti-Periplanar Compound

Anti-periplanar and syn-periplanar are two words used in organic chemistry. Both terms refer to the form of chemical bonds in a molecule.

A planar dihedral compound has a dihedral angle between 150 and 180 degrees between two atoms or groups of atoms. In this configuration, the groups are anti-coplanar.

Butane (C4H10) is shown in a periplanar syn conformation with two methyl groups (-CH3) positioned at an angle of 180 degrees.

E2 Mechanism

A bimolecular elimination process occurs when the carbon-hydrogen bond is broken and the leaving group is placed in the anti-plane.

For E2 to occur, the hydrogen and leaving group must be anti-planetary. Simply put, the hydrogen group and the leaving group must lie in the same plane, but in different directions, creating a "Z" configuration involving two carbons.

The Pinacol Rearrangement

The methyl group appears to be anti-planar to the active alcohol function of the pinacol rearrangement. The rearrangement reaction takes its name from the conversion of pinacol to pinacolone.

Pinnacles are chemicals with two hydroxyl groups, one on each adjacent carbon atom. It is a white solid organic matter.

The pinacol rearrangement favours the synthesis of spirocyclic ketones when cyclic diol precursors are used. This type of rearrangement produces many spiro ring molecules. A chiral centre is constructed near the heterocycle using a pinnacles rearrangement.

Misuse, Etymology And Historiography

Klein and Perilog first defined the term antiperiplanar in their 1960 paper "Explanation of Spatial Connections Across Single Bonds". Two functional groups on the opposite side of the bond face are called "anti". Periplanar is derived from the Greek word peri meaning "almost flat". According to Kane and Hersh, many organic textbooks use anti-peripheral plane to mean full-plane anti-plane or anti-coplanar, which is technically incorrect.

Molecular Orbital

One of the key elements of antiperiplanar structure is the interaction between molecular orbitals. Antiperiplanar geometries place the bonding and antibonding orbitals nearly parallel or coplanar. 2-chloro-2,3-dimethylbutane shows the C-H σC-H bond orbital and the C-Cl σ*C-Cl anti-bond orbital, syn-periplanar. Parallel orbitals do overlapping . They also show their participation in hyperconjugation. If the bonding orbital is electron donating and the antibonding orbital is electron accepting, a bonding orbital can donate electronegativity to an antibonding orbital. This charged-to-uncharged acceptor-donor interaction has an overall stabilizing effect on the molecule. However, donating from a bonding orbital to an antibonding orbital also results in a weakening of both bonds. 2-chloro-2,3-dimethylbutane is stabilized by hyperconjugation via electron donation from σC–H to σ*C–Cl, but both the C–H and C–Cl bonds are weakened. Molecular orbital diagrams show that mixing σC-H and σ*C-Cl in 2-chloro-2,3-dimethylbutane lowers the energy of both orbitals.