[khemikool]

Is there always an even number of curly arrows in used in an individual step to illustrate mechanisms since as bonds break others are formed and vice versa or can there be an odd number of curly arrows used as well? I ask because I am trying to see if it is possible to develop a general approach when drawing mechanisms instead of having to memorize specific aspects of each mechanism for tests.

[sjb]

Is there always an even number of curly arrows in used in an individual step to illustrate mechanisms since as bonds break others are formed and vice versa or can there be an odd number of curly arrows used as well? I ask because I am trying to see if it is possible to develop a general approach when drawing mechanisms instead of having to memorize specific aspects of each mechanism for tests.

Consider for instance the enamine - imine isomerisation in the Fischer indole synthesis

[Dan]

Is there always an even number of curly arrows in used in an individual step to illustrate mechanisms since as bonds break others are formed and vice versa or can there be an odd number of curly arrows used as well? I ask because I am trying to see if it is possible to develop a general approach when drawing mechanisms instead of having to memorize specific aspects of each mechanism for tests.

No, there can be an odd or even number. Other examples of odd numbers are the Diels-Alder reaction, elimination and conjugate addition reactions.

Take a logical approach to organic mechanism, you can't cut corners with generalisations. Looking for a general rule is memorisation - predicting the reactivity by developing a good understanding of the principles behind the way electrophiles, nucleophiles, acids and bases behave will limit the need for memorisation.