Robinson arrows

By convention, the shift of electron pairs is indicated by special arrows called the Robinson arrow, in the honor of Robert Robinson, the chemist who developed the theory of chemical reaction mechanisms. 

Robinson won the 1947 Nobel Prize in chemistry for his studies of natural prod ucts He may also have been the first to use curved arrows to track electron movement... 

In 1925, Robinson first published his schematic "curly arrows," indicating electron drift or displacement, 124, defining nitrosobenzene as a crotenoid reactant. 

Shortly after Ingold received the preprint of the 1926 paper, he sent a paper to the Chemical Society which was published later in 1926. Here he dealt with the nitration of ortho aminophenol derivatives, adopting the kind of explanation that appeared in Robinson s paper and rationalizing the meaning of the so-called free and bound affinity, which he and Fliirscheim previously had been employing, by the new electronic interpretation. As discussed in chapter 8, the paper included Robinson s curved arrows but introduced a new delta (d) notation for polarity as well as other new terms. 126 The Manchester group referred to this paper as "Ingold s conversion." 127... 

Labelled reticuline was readily incorporated into thebaine 14, codeinone 15a, codeine 15b, and morphine 16 without scrambling of the labels. Salutaridine is not present in detectable quantities in Papaver somniferum. However, when appropriately labelled, it is well incorporated into morphine alkaloids. Salutaridine can be readily reduced to two stereo-isomeric allylic alcohols 17, both of which are converted by mild acid catalysis (17, see arrows) to give thebaine 14. The alkaloids 17, 14, 15a, and 15b were all shown to be precursors of morphine. This was of interest, because the earlier theory of Robinson suggested that unmethylated alkaloids were first assembled and methylation was a terminal stage of biosynthesis. 

The reason was the first ever use of curly or curved arrows, in this case to represent tautomerism in A,A-dimethylamino derivatives. While the arrows were not then meant to indicate movement of electrons (as was later universal in the electronic theory of organic reactions), it is most probable that the symbols were adopted by Robert Robinson who, with Watson, worked at British Dyes during World War I123. Arthur Lapworth and Alfred Werner had already used arrows in mechanistic studies, the former perhaps influenced by the inventor of the TNA process, Bernard J. FlUrscheim, who explained benzene substitution patterns in terms of affinity demand , indicated by arrowed bonds124. 

Early depictions relevant to the development of the electronic theory of organic chemistry A) representation of the reaction between 1,3-butadiene and Br2, in the manner of Robinson, depicting partial bonds and polarities B) the "birth of the Robinson-Kemack curly arrows representing partial valences in 1,3-butadiene C) application by Robinson of curly arrows toward the explanation of meta substitution in nitroso benzene D) early representations by Thiele and others of the equivalence of all bonds in benzene E) Robinson s 1925 representation of benzene... 

Figure 17.3. Robinson showed how benzene reactivity could be understood in terms of mobile electrons moving around the benzene ring. He used arrows to show electron movements.

Write mechanism arrows for the following step in the chemical synthesis by A. Robertson and R. Robinson (/. Chem. Soc. 1928, 1455—1472) of callistephin chloride, a red flower pigment from the purple-red aster. Explain why this transformation is a reasonable process. 

Figure 7-10 Collected values of average eddy diffusivity in pipe center. Arrows indicate spread of data curves 1, 2, van Zoorev (1962) curve 3, McCarter, Stutzman, and Koch (1949) curve 4, Schlinger and Sage (1953) curve 5, Towle and Sherwood (1939) curve 6, Baldwin and Mickelson (1963) curves 7, 8, Boothroyd (1967) curves 9, 10, Soo, Ihrig, and El Kouch (1960) (gas), Briller and Robinson (1969) + (fine particles), Boothroyd (1971). Reproduced with permission of Taylor and Frances, Ltd.

Sir Robert Robinson played an early central role in the development of the electronic theoiy of organic chemistry (5S). For example, he was the first to use the now commonplace curly arrow to imply the reorganization of electron density during the course of a chemical reaction (59). The constract of stereoelectronic control (which, in its most literal sense, explains all chemical reactions) underpins many concepts now in the lexicon of mechanistic and synthetic organic chemistry. These include the Hammond postulate, the Curtin-Hammett Principle, the Markovnikov rule (for additions to alkenes), the Thorpe-lngold effect (on rates of cyclization), the Btirgi-Dunitz approach trajectory, Cram/Comforth/Felkin-Ahn controlled additions (to chiral ketones... 

An annulation is a reaction in which a new ring is formed. The Robinson annulation is named for English chemist Sir Robert Robinson (1886-1975). It consists of a series of two reactions that use the same catalyst. Under each reaction arrow write the name of a reaction we have studied recently. 

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. ... 

---