Full-headed curved arrow

Double-headed arrow Full-headed curved arrow Half-headed curved arrow (fishhook)... 

Full-headed curved arrow (Section 6.3B) An arrow used in a reaction mechanism to denote the movement of a pair of electrons. 

Full-Headed Curved Arrow Moves Two Electrons Half-Headed Curved Arrow Moves One Electron Electron Source Electron Sink Charge Is Conserved Direction of Electron Flow Good Arrow Pushing Habits Common Errors... 

A full-headed curved arrow indicates the movement of two electrons from the tail of the arrow to the head. A half-headed curved arrow indicates the shift of one electron likewise. The two ways that a bond can break are heterolytic (two electrons) or homolytic (one electron). Homolytic processes are unusual and will be treated separately in Chapter 11. 

Well develop the point in more detail later, but you might note for now that the movement of one electron in the symmetrical process is indicated using a half-headed, or "fishhook," arrow (a), whereas the movement of two electrons in the unsymmetrical process is indicated using a full-headed curved arrow (Ai). 

Sample Problem 6.1 Use full-headed or half-headed curved arrows to show the movement of electrons in each equation. 

As we saw in Section 2.11, chemists indicate the movement of an electron pair during a polar reaction by using a curved, full-headed arrow. A curved arrow shows where electrons move when reactant bonds are broken and product bonds are formed. It means that an election pair moves from the atom... 

Curved arrowrs with full heads are used to describe the breaking of bonds and the formation of new ones in chemical reactions. Half-headed arrows are introduced to cover reaction situations where pairs of electrons forming bonds are supposed to move in different directions and join up in new pairings. 

Figure 11. Antijunctions and mesojunctions. (a) A 949 knot drawn in a DNA context. Each of the nodes of this knot is shown to be formed from a half-turn of double helical DNA. The polarity of the knot is indicated by the arrowheads passing along it. Various enclosed areas contain symbols indicating the condensation of nodes to form figures. The curved double-headed arrow indicates the condensation of two half-turns into a full turn, the solid triangle indicates a three-arm branched junction, the empty square indicates a 4-strand antijunction, and the shaded square is a four-strand mesojunction. (b) Schematic drawings of 3-strand and 4-strand junctions, antijunctions, and mesojunctions shown as the helical arrangements that can flank a triangle or a square. Each polygon is formed from strands of DNA that extend beyond the vertices in each direction. The arrowheads indicate the 3 ends of the strands. The vertices correspond to the nodes formed by a half-turn of double helical DNA. Base pairs are represented by lines between antiparallel strands. Thin double-headed arrows perpendicular to the base pairs represent the axis of each helical half-turn. The lines perpendicular to the helix axes terminating in ellipses represent the central dyad axes of the helical half-turns. The complexes 33 and 44 correspond to conventional branched junctions. The complex 40 is a 4-strand antijunction. The complexes on the bottom row are mesojunctions, which contain a mix of the two orientations of helix axes.

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