Double-headed curved arrow

Double- and single-headed curved arrows indicate the movement of electrons. Double-headed curved arrows (shown in Figure 2-4a) show the movement of two electrons, whereas single-headed curved arrows (Figure 2-4b) indicate the movement of one electron. The electrons always move in the direction indicated by the arrow. The head (point) of the arrow is where the electron is going, and the tail is the electron s source. [Pg.18]

Double-headed arrow Full-headed curved arrow Half-headed curved arrow (fishhook)... [Pg.205]

Fig. 6. Discharge behavior of a battery where is the open circuit voltage (a) current—potential or power curve showing M activation, ohmic, and M concentration polarization regions where the double headed arrow represents polarization loss and (b) voltage—time profile.

These difficulties have led to the convention of representing molecules that cannot adequately be written as a single classical structure by a combination of two or more classical structures, the so-called canonical structures, linked by a double-headed arrow. The way in which one of these structures can be related to another often being indicated by curved arrows, the tail of the curved arrow indicating where an electron pair moves from and the head of the arrow where it moves to ... [Pg.19]

We shall, however, subsequently write canonical structures, e.g. (19a) and (19b), linked by a double-headed arrow, but without curved arrows. These will be reserved for indicating a real movement of electron pairs, i.e. as happens during the forming, and breaking, of bonds in the course of a real reaction. [Pg.19]

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.

Some atoms, even in covalent compounds, carry a formal charge, defined as the number of valence electrons in the neutral atom minus the sum of the number of unshared electrons and half the number of shared electrons. Resonance occurs when we can write two or more structures for a molecule or ion with the same arrangement of atoms but different arrangements of the electrons. The correct structure of the molecule or ion is a resonance hybrid of the contributing structures, which are drawn with a double-headed arrow () between them. Organic chemists use a curved arrow (O) to show the movement of an electron pair. [Pg.1]

Fig. 4 Cartoons representing a [2]catenane and a [2]rotaxane. The arrows show the main possible large-amplitude movements of one component with respect to the other pirouetting (curved arrows) and shuttling (double-headed arrow)...

We use a single double-headed arrow between resonance forms (and often enclose them in brackets) to indicate that the actual structure is a hybrid of the Lewis structures we have drawn. By contrast, an equilibrium is represented by two arrows in opposite directions. Occasionally we use curved arrows (shown in red above) to help us see how we mentally move the electrons between one resonance form and another. The electrons do not actually resonate back and forth they are delocalized over all the resonance forms at the same time. [Pg.1321]

A blank titration curve can be easily calculated, and, at least in the nearly neutral pH range, the experimental curves do not differ much from theoretical predictions. A blank titration of a supernatant obtained at a natural pH rather than of pure electrolyte was recommended in [522]. The raw surface charge density is obtained by subtraction of the volume (number of moles) of acid or base (1 mole of base is equivalent to minus 1 mole of acid double-headed arrows in Figure 2.6) that was used to bring about the same pH in tlie dispersion on the one hand and in the electrolyte solution on the other that is. [Pg.67]

Figure 16.10. Oriented PP. Load cycling monitored by SAXS. Circular dots show where SAXS patterns have been recorded. Numerical labels indicate their sequence. The highlighted part of the curve near label 11 Indicates the part traversed during the recording of pattern 11. The drawing direction with respect to the patterns, S3, is indicated by a double-head arrow ( Reproduced [48] with permission of Wiley-VCH)...

Figure 1.27. (a) Double-headed arrow, used for resonance forms only. The material A on the left has a different-type font than that on the right. They are different representations of the same letter and both are correct, (b) Two arrows, generally used to indicate equilibriinn. These two arrows are not to be used for resonance. A and B are different from each other, (c) Curved arrows, indicating movement of an electron pair. A pair of electrons originating on A is used to form a bond from A to B. A new compound is formed ( A-B ), and A has become poorer in electrons (they were used to make the bond) and B has become richer. [Pg.42]

All representations of the structures reached by the curved-arrow approach and connected with double-headed arrows must have all atoms in the same positions in space. Only electron motion is considered. [Pg.43]

In Eq. (55), the double-headed arrow indicates that the actual state of the molecule is between the two extreme or resonance forms as shown. The shift in electrons, shown by the curved arrows, is now in a direction opposite... [Pg.139]

Fig. 17.46a,b. Turf toe. Schematic drawings illustrate the pathomechanism of this condition, a During normal dorsiflexion of the first metatarsophalangeal joint, the plantar plate (asterisk) is subjected to stretching forces (double-headed arrow) as a result of tension applied to the plantar capsule, b With excessive extension (curved white arrows), the metatarsal neck (MH) impinges on the base of the proximal phalanx (Ph) and transmits excessive tension (double-headed arrow) to the plate causing its disruption. [Pg.875]

Fig. 27. Contour diagram of the collinear H + H2 potential energy surface, with the symmetric and as3rmmetric stretch vibrations of the saddle point configuration indicated by double-headed arrows. These vibrations are associated with the first two resonances in the P q curve of Fig. 2 these resonances represent virtual states embedded in the scattering continuum.

An example of a bond-to-bond step is shown in Figure 2-6. The tail of the curved arrow begins at one of the bonding pairs of the double bond (the TT-bond), while the head points to where the new tt-bond will form. [Pg.21]

Resonance forms differ only in the placement of their tt or nonbonding electrons. Neither the position nor the hybridization of any atom changes from one resonance form to another. In nitromethane, for example, the nitrogen atom is s/j -hybridized and the oxygen atoms remain in exactly the same place in both resonance forms. Only the positions of the tt electrons in the N=0 double bond and the lone-pair electrons on oxygen differ from one form to anothor. This movement of electrons on going from one resonance structure to another is sometimes indicated by using curved arrows. A curved arrow always indicates the movement of electrons, not the movement of atoms. An arrow shows that a pair of electrons moves from the atom or bond at the tail of the arrow to the atom or bond at the head of the arrow. [Pg.66]

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