Search results
Results from the WOW.Com Content Network
However, the electron-rich π system above and below the benzene ring hosts a partial negative charge. A counterbalancing positive charge is associated with the plane of the benzene atoms, resulting in an electric quadrupole (a pair of dipoles, aligned like a parallelogram so there is no net molecular dipole moment).
While benzene does not have a dipole moment, it has a strong quadrupole moment. [8] The local C–H dipole means that there is positive charge on the atoms in the ring and a correspondingly negative charge representing an electron cloud above and below the ring.
[1] [2] [3] It provides the theoretical basis for Hückel's rule that cyclic, planar molecules or ions with + π-electrons are aromatic. It was later extended to conjugated molecules such as pyridine, pyrrole and furan that contain atoms other than carbon and hydrogen (heteroatoms). [4]
In chemistry, π-effects or π-interactions are a type of non-covalent interaction that involves π systems.Just like in an electrostatic interaction where a region of negative charge interacts with a positive charge, the electron-rich π system can interact with a metal (cationic or neutral), an anion, another molecule and even another π system. [1]
Hückel's rule can also be applied to molecules containing other atoms such as nitrogen or oxygen. For example pyridine (C 5 H 5 N) has a ring structure similar to benzene, except that one -CH- group is replaced by a nitrogen atom with no hydrogen. There are still six π electrons and the pyridine molecule is also aromatic and known for its ...
Oppositely, withdrawing electron density is more favourable: (see the picture on the right). The -M effect of the nitroso group. As a result, the nitroso group is a deactivator. However, it has available to donate electron density to the benzene ring during the Wheland intermediate, making it still being an ortho / para director.
For example, the following hydrogen atom migration is of order [1,5], attained by counting counterclockwise through the π system, rather than the [1,3] order designation through the ring CH 2 group that would mistakenly result if counted clockwise. As a general approach, one can simply draw the transition state of the reaction.
In chemistry, charge-transfer (CT) complex, or electron donor-acceptor complex, describes a type of supramolecular assembly of two or more molecules or ions. The assembly consists of two molecules that self-attract through electrostatic forces, i.e., one has at least partial negative charge and the partner has partial positive charge, referred ...