Organic Chemistry

Conformations

Different spatial arrangements of a molecule that are generated by rotation about single bonds.

 

Rotation about C-C single bonds is very fast, hundreds of thousands of times per second at room tempterature. 

Conformational analysis
The study of how ________ factors affect the structure of a molecule and its physical, chemical, and biological properties.
Staggered confirmation
Conformation of the type in which the bonds on adjacent carbons are as far away from one another as possible
Eclipsed confirmation
Conformation in which bonds on adjacent atoms are aligned with one another.
Gauche
Term describing the position relative to each other of two substituents on adjacent atoms when the angle between their bonds is on the order of 60 degrees.
Anti
Term describing relative position of two substituents on adjacent atoms when the angle between their bonds is on the order of 180 degrees
Torsional strain
Decreases stability of a molecule associated with eclipsed bonds.
Steric strain
Destabilization of a molecule as a result of van der Waals repulsion, distorted bond distances, bond angles, or torsion angles.
Activation energy
Molecules must become energized to undergo a chemical reaction. Kinetic (thermal) energy is absorbed by a molecule from collisions with other molecules and transformed into potential energy
Transition state
The point of maximum potential energy in an elementary step of a reaction mechanism as they proceed to products.
van der Waals strain
Destabilization that results when two atoms or groups approach each other too closely. Also known as ___ __ _____ repulsion.
Steric hindrance
An effect on structure or reactivity that depends on van der Waals repulsive forces
Angle strain
The strain a molecule possesses because its bond angles are distorted from their normal values
Half-chair
One of the two most stable conformations of cyclopentane. Three consecutive carbons in the half-chair conformation are coplanar. The fourth and fifth carbon lie, respectively, above and below the plane.
Envelope
One of the two most stable conformations of cyclopentane. Four of the carbons in the envelope conformation are coplanar; the fifth carbon lies above or below this plane.
Chair
The most stable conformation of cyclohexane
Boat
An unstable conformation of cyclohexane
Twist boat/skew boat
An unstable conformation of cyclohexane. It is slightly more stable than the boat conformation
Axial hydrogens
the Hs are bonded parallel to a vertical axis
Equatorial hydrogens
the Hs are bonded along the molecule’s “equator”
Ring inversion, chair-chair introversion, ring flipping
One chair conformation is converted to another chair
Intermediate
Transient species formed during a chemical reaction. Typically, an intermediate is not stable under the conditions of its formation and proceeds further to form the product. Unlike a transition state, which corresponds to a maximum along a potential energy surface, an intermediate lies at a potential energy minimum.
1,3-diaxal repulsions
n
cis

trans

this side

across

Stereoisomers
Isomers with the same constitution but that differ in respect to the arrangement of their atoms in space.
Bridged compound

Two atoms are common to two (or more) rings.

;

Numbering starts with the largest bridge, then middle, then shortest.;

Spiro compound

A compound in which a single carbon is common to two rings.

;

The rings are at right angles to each other.

;

Simplest example is ___ [2.2] pentane;

Heterocycle
A ring that contains at least one herteratom is called a _____.; A subtance that includes an atom other than carbon, called a heteroatom, as part of a ring.
Heterocyclic compound
Cyclic compound in which one or more of the atoms in the ring are elments other than carbon. Heterocyclic compounds may or may not be aromatic. Many contain double bonds. The ;other; atoms are commonly O, N, and S.
Fused ring compound;; ;;

Under bridged ring category.

Two rings share a common side.;

Bridge is common side, counts for zero atoms.;

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