In the first reaction step, the amine's unshared electron pair adds to the electron-deficient carbonyl carbon while one electron pair from its C=0 double bond transfers to the oxygen atom. Following tautomer- ization (the shift of a hydrogen atom), the unshared electron pair on the nitrogen atom of the carbinolamine intermediate adds to the electron- deficient carbon atom with the elimination of a hydroxide ion. Familiarity with the relative electronegativities of atoms While it is sometimes sufficient to draw the structures of a reaction's substrates and products, a full understanding of the reaction mecha- nism requires knowing how electrons are reallocated as covalent bonds are broken and re-formed. Biochemists use the curved arrow conven- tion to show how pairs of electrons are rearranged during a reaction. Although single-electron reactions also occur in biochemistry, we wll focus on the more common two-electron reactions. The moverment of an electron pair (which may be either a lone pair or a pair forming a covalent bond) is symbolized by a curved arrow emanating from the electron pair and pointing to the electron-deficient center attracting the electron pair. For example, bond breakage is O> N» C- H may be helpful in predicting the movement of electrons, since electrons- either those in covalent bonds or in lone pairs tend to move from less electronegative atoms toward more electronegative atoms. Showing lone electron pairs as dots can help identify electron-poor and electron-rich atoms. In addition, the rules of chemical reason apply to the system: For example, there are never five bonds to a carbon atom or two bonds to a hydrogen atom. shown as x+ + Y and bond formation as X-Y An example of a more complicated reaction requiring several curved arrows is the formation of an imine (Schiff base), a biochemically impor- tant reaction between an amine and an aldehyde or ketone: H R' H R' H R H R' tautomerization R-N; + R-N*-C- R-N,C-oH + OH H R" H R" R" R R' Amine Aldehyde Carbinolamine intermediate Imine (Schiff base) or ketone

In the first reaction step, the amine's unshared electron pair adds to the electron-deficient carbonyl carbon while one electron pair from its C=0 double bond transfers to the oxygen atom. Following tautomer- ization (the shift of a hydrogen atom), the unshared electron pair on the nitrogen atom of the carbinolamine intermediate adds to the electron- deficient carbon atom with the elimination of a hydroxide ion. Familiarity with the relative electronegativities of atoms While it is sometimes sufficient to draw the structures of a reaction's substrates and products, a full understanding of the reaction mecha- nism requires knowing how electrons are reallocated as covalent bonds are broken and re-formed. Biochemists use the curved arrow conven- tion to show how pairs of electrons are rearranged during a reaction. Although single-electron reactions also occur in biochemistry, we wll focus on the more common two-electron reactions. The moverment of an electron pair (which may be either a lone pair or a pair forming a covalent bond) is symbolized by a curved arrow emanating from the electron pair and pointing to the electron-deficient center attracting the electron pair. For example, bond breakage is O> N» C- H may be helpful in predicting the movement of electrons, since electrons- either those in covalent bonds or in lone pairs tend to move from less electronegative atoms toward more electronegative atoms. Showing lone electron pairs as dots can help identify electron-poor and electron-rich atoms. In addition, the rules of chemical reason apply to the system: For example, there are never five bonds to a carbon atom or two bonds to a hydrogen atom. shown as x+ + Y and bond formation as X-Y An example of a more complicated reaction requiring several curved arrows is the formation of an imine (Schiff base), a biochemically impor- tant reaction between an amine and an aldehyde or ketone: H R' H R' H R H R' tautomerization R-N; + R-N*-C- R-N,C-oH + OH H R" H R" R" R R' Amine Aldehyde Carbinolamine intermediate Imine (Schiff base) or ketone

Organic Chemistry

9th Edition

ISBN:9781305080485

Author:John E. McMurry

Publisher:John E. McMurry

Chapter23: Carbonyl Condensation Reactions

Section23.SE: Something Extra

Problem 45MP

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