Organic shorthand

Where changes in appearance are of paramount interest, as in the case of metallic and organic coatings on steel or other metals, visual examination is most desirable. To facilitate ratings on such a basis, photographic standards have been employed, as, for example, in tests on chromium-plated steel undertaken by ASTM Committee B-8 on Electrodeposited Metallic Coatings . These ratings are supplemented by a shorthand description of the nature of the deterioration observed. 

Since carbon has four bonds to fill, and because hydrogen is the most likely atom to be attached to carbon in an organic molecule, chemists invented a shorthand notation that is easier to read and draw. 

Continuous flow stirred tank reactors are normally just what the name implies—tanks into which reactants flow and from which a product stream is removed on a continuous basis. CFSTR, CSTR, C-star, and back-mix reactor are only a few of the names applied to the idealized stirred tank flow reactor. We will use the letters CSTR as a shorthand notation in this textbook. The virtues of a stirred tank reactor lie in its simplicity of construction and the relative ease with which it may be controlled. These reactors are used primarily for carrying out liquid phase reactions in the organic chemicals... 

The shorthand symbol for organic groups is i - Technical writers (and chemistry teachers) use R- whenever they want to indicate that any number of organic groups could be attached to make a molecule. In Figure 1—7, the methyl group, -CH3, could be represented by R-. 

The study of carbon compounds provides us with the subdivision organic chemistry , and a few simple organic compounds can exempMfy this shorthand approach to molecular representations. The primary alcohol propanol (systematically propan-l-ol or 1-propanol, formerly n-propanol, n signifying normal or unbranched) can be represented by a stmcture showing all atoms, bonds, and lone pair or nonbonding electrons. 

In the chemists shorthand for organic structures, each vertex is a carbon atom. If fewer than four bonds to that carbon are shown, it is understood that H atoms are attached to the carbon so that it makes four bonds. 

We can see the different structural features of n-pentane, Ao-pentane, and neo-pentane more clearly by drawing the molecules in two dimensions, as shown in the middle row of Figure 12.1. Alternatively, we can represent them by the stick structures shown in the bottom row. A stick structure is a commonly used, shorthand notation for representing an organic molecule. Each line (stick)... 

The structural formula is also a shorthand notation for the important chemical reactions of lhe compound. Ii can be considered as being built up of a group of organic radicals, i.e.. groups of atoms that retain their individuality in the course of certain reactions. Each radical has reactions which are characteristic of its presence in the molecule. 

Finally, it should be stressed that organic electron transfers only rarely occur as isolated steps because of the high chemical reactivity of odd-electron species. Normally, they are part of multi-step mechanisms together with other types of elementary reaction, such as bond forming and breaking. In organic electrochemistry a useful shorthand nomenclature for electrode mechanisms denotes electrochemical (= electron transfer) steps by E and chemical ones by C, and it is appropriate to use the same notation for homogeneous electron-transfer mechanisms too. Thus, an example of a very common mechanism would be the ECEC sequence illustrated below by the Ce(IV) oxidation of an alkylaromatic compound (14-17) (Baciocchi et al., 1976,... 

Several kinds of formulas are used by organic chemists to represent organic compounds. Some of these formulas involve a shorthand notation that requires some explanation. Structural formulas actually show which atoms are bonded to which. There are two types of structural formulas, complete Lewis structures and condensed structural formulas. In addition, there are several ways of drawing condensed structural formulas. As we have seen, a Lewis structure symbolizes a bonding pair of electrons as a pair of dots or as a dash (—). Lone pairs of electrons are shown as pairs of dots. 

Other units that you may encounter, especially in connection with spectroscopic data are for wavelength. Angstrom (A 1 A = 0.1 nm) for energy, electron volt (eV 1 eV = 96.5 k mol- ) for wavenumber (v = X- ), reciprocal centimetre (cm ). Sometimes cm is employed as though it were an energy unit, but this is only a convenient shorthand. Some organic photochemists still use calorie (cal 1 cal = 4.18 ) as their preferred energy unit. 

Figure 4 A possible scheme for the catal)rtic reactions of diiron sites in the 02-activating enzymes. Formal oxidation states, groimd spin states, and shorthand letter designations are hsted below each diiron species. Except for tyrosyl (in RNR), the depiction of organic radicals is hypothetical (Ref. 22, 1997 Springer Verlag)...

Because more complicated organic compounds contain many carbon atoms, organic chemists have devised a shorthand to draw them. Keep in mind the following when examining these structures ... 

To understand the structure of palytoxin we need to know more shorthand for drawing chains of organic molecules. The following conventions are often used. 

Important topics in Chapter 1 include drawing Lewis structures, predicting the shap)e of molecules, determining what orbitals are used to form bonds, and how electronegativity affects bond polarity. Equally important is Section 1.7 on drawing organic molecules, both shorthand methods routinely used for simple and complex compounds, as well as three-dimensional representations that allow us to more clearly visualize them. 

Drawing organic molecules presents a special challenge. Because they often contain many atoms, we need shorthand methods to simplify their structures. The two main types of shorthand representations used for organic compounds are condensed structures and skeletal structures. 

Shorthand methods are used to abbreviate the structure of organic molecules. 

Skeletal structure (Section 1.7B) A shorthand representation of the stmcture of an organic compound in which carbon atoms and the hydrogen atoms bonded to them are omitted. All heteroatoms and the hydrogens bonded to them are drawn in. Carbon atoms are assumed to be at the junction of any two lines or at the end of a line. 

---