Fishhook curly arrow

In the formation of radicals, a bond is broken and each atom takes one electron from the pair constituting the bond. Bond-making and bond-breaking processes are indicated by single-headed (fishhook) curly arrows representing the movement of one electron. 

Notice the use of single-headed (or fishhook) curly arrows to represent the movement of single electrons (Section 4.1)... 

A single-headed curly arrow or fishhook arrow indicates the movement of a single electron. 

Here, we have used single-headed curly arrows or fishhook arrows to indicate. the movement of single electrons. The tail of the curly arrow shows the source of the electron and the head shows its destination. Using single-headed curly arrows, the mechanism for the methane/chlorine chain reaction is completed below. 

It makes good sense to draw free-radical mechanisms in the manner shown by these examples. However, shorter versions may be encountered in which not all of the arrows are actually drawn. These versions bear considerable similarity to two-electron curly arrow mechanisms, in that a fishhook arrow is shown attacking an atom, and a second fishhook arrow is then shown leaving this atom. The other electron movement is not shown, but is implicit. This type of representation is quite clear if the complement of electrons around a particular atom is counted each time but, if in any doubt, use all the necessary fishhook arrows. 

Pericyclic reactions are the third distinct class. They have cyclic transition structures in which all bond-forming and bond-breaking takes place in concert, without the formation of an intermediate. The Diels-Alder reaction and the Alder ene reaction are venerable examples. The curly arrows can be drawn in either direction—clockwise, as here, but equally well anti- clockwise. They could even be drawn with fishhook arrows, and would still... 

Electron movement is symbolized by a double-headed curly arrow for the movement of an electron pair, and a single-headed arrow or fishhook for the movement of a single electron. In representing electron movement, the arrow must start from the bond or atom that provides the electron(s) and the arrow should end where the electron movement terminates, either to form a bond or on the particular atom or group that receives the charge. Thus if the electron movement creates a bond,... 

Curly arrows can be used to represent bond cleavage. A double-headed arrow represents the movement of two electrons (and is used in ionic mechanisms). A single-headed arrow (or fishhook) is used to represent the movement of a single electron (and is used in radical mechanisms). Curly arrows therefore always depict the movement of electrons. Heterolysis (use one double-headed arrow)... 

It is also deduced that the mechanisms for ground-state and excited state base displacement reactions cannot proceed via movements of pairs of electrons in concert, i.e. the fishhook arrow for a one-electron transfer replaces the curly arrow for concerted electron-pair transfer (see Chapter 21, Addendum 3). 

Robinson s curly arrow is used to show the movements of pairs of electrons in a reaction mechanism. The tail of a curly arrow starts at a mobile electron pair and its head points to the destination of the electron pair. Fishhook arrows indicate cleavage or movement of a single electron shown as a single-headed curved arrow. They are widely used in radical chemistry to represent the homolytic cleavage and reactions of radicals. ... 

In Refs. 14(d,f),21, comparisons are made between the above curly arrow and fishhook arrow formulations of base displacement reactions. One of them involves the formation of the [X R]C + y excited state of the products via the dissociation of the reactant-like complex using one-electron transfers, as in... 

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