Ring two carbons

NMR reveals all the different carbon nuclei Carbon skeleton No C=0 group ten carbons in aromatic rings two carbons next to 0 three other saturated C atoms... 

As can be seen, this algorithm additionally identifies constitutionally equivalent atoms. These are atoms with the same EC value (3) in the final iteration, such as the two carbon atoms in the ortho positions of the phenyl ring with an EC value of 9 (Figure 2-44). 

The bivalent radical —NH— linked to two identical radicals can be denoted by the prefix imino-, as well as when it forms a bridge between two carbon ring atoms. A trivalent nitrogen atom linked to three identical radicals is denoted by the prefix nitrilo-. Thus ethylenediaminetetraacetic acid (an allowed exception) should be named ethylenedinitrilotetraacetic acid. 

An oxygen atom directly attached to two carbon atoms already forming part of a ring system or to two carbon atoms of a chain may be indicated by the prefix epoxy-. For example, CH2—CH—CH2CI is named l-chloro-2,3-epoxypropane. 

In presence of—C=C— or of aromatic ring In presence of—C=0 bond In presence of two carbon-oxygen bonds In presence of two carbon-carbon double bonds Aryl-C=0... 

This is the branch-poiat differentiatiag phenylalanine (25, R = H) from tyrosiae (25, R = OH). Both phenylalanine and tyrosiae contain an aryl ring, a three-carbon side chain (a Cg—Cg fragment), and a nitrogen. Decarboxylation yields a two-carbon side chain (a Cg—Cg fragment), eg, 2-phenethylamine (59, R = H) from phenylalanine and tyramine (59, R = OH) from tyrosiae, although it is not certain that ia all cases decarboxylation must precede use ia alkaloid constmction. 

The two carbons that bear no numbers are common to both rings and carry no hydrogen atoms. From the symmetrical configuration of the naphthalene molecule, it should be possible for only two isomers to exist when one hydrogen atom is replaced by another atom or group. Therefore, positions 1, 4, 5, and 8 are identical and often are designated as "a" positions likewise, positions 2, 3, 6, and 7 are identical and are designated as "P" positions, as shown in (2). 

Symmetrical diaLkyl peroxides are commonly named as such, eg, dimethyl peroxide. For unsymmetrical diaLkyl peroxides, the two radicals usually are hsted ia alphabetical order, eg, ethyl methyl peroxide. For organomineral peroxides or complex stmctures, ie, where R and R are difficult to name as radicals, the peroxide is named as an aLkyldioxy derivative, although alkylperoxy is stUl used by many authors. CycHc peroxides are normally named as heterocychc compounds, eg, 1,2-dioxane, or by substitutive oxa nomenclature, eg, 1,2-dioxacyclohexane however, when the two oxygens form a bridge between two carbon atoms of a ring, the terms epidioxy or epiperoxy are frequendy used. The resulting polycycHc stmcture has been called an endoperoxide, epiperoxide, or transaimular peroxide. 

Substitution of two carbon atoms of a benzene ring by tervalent nitrogen atoms may occur in three ways, giving rise to pyridazines (see Chapter 2.12), the pyrimidines (see Chapter 2.13) and the pyrazines, with the nitrogen atoms occupying a 1,2-, 1,3- or 1,4-disposition respectively. 

A pyrrole-like nitrogen in a ring iV-methyl group gives a peak around -220 p.p.m. if adjacent to two carbon atoms one or two neighboring nitrogens shift the peak downfield by about 40 and 90 p.p.m., respectively. 

Dipolarophiles utilized in these cycloadditions leading to five-membered heterocycles contain either double or triple bonds between two carbon atoms, a carbon atom and a heteroatom, or two heteroatoms. These are shown in Scheme 9 listed in approximate order of decreasing activity from left to right. Small rings containing a double bond (either C=C or C=N) are also effective dipolarophiles, but these result in six- and seven-membered ring systems. 

Early efforts to partially synthesize 20-keto and 17a-hydroxy-20-keto steroids led to ring D-expanded products isomeric with the desired compounds. Darzens condensation of 3/5-hydroxyandrost-5-en-17-one acetate (75) with ethyl a,a-dichloropropionate, followed by alkali treatment and decarboxylation, gives both the expected 3j5-hydroxypregn-5-en-20-one (78) and an isomer now known to be 17a-methyl-D-homo-17-ketone (79).36,37a alternative route for the introduction of the two carbon side chain, Ruzicka... 

Strong sp -sp a bonds are not possible for cyclopropane, because the 60° bond angles of the ring do not permit the orbitals to be properly aligned for effective overlap (Figure 3.10). The less effective overlap that does occur leads to what chemists refer to as bent bonds. The electron density in the carbon-carbon bonds of cyclopropane does not lie along the internuclear- axis but is distr-ibuted along an arc between the two carbon atoms. The r-ing bonds of cyclopropane are weaker than other carbon-carbon a bonds. 

Polycyclic hydrocarbon (Section 3.14) A hydrocarbon in which two carbons are common to two or more rings. 

A similar sequence of reactions takes place with the enamlnes of cyclic ketones (55-57) the initially formed unstable cyclobutene rearranges with insertion of two carbon atoms into the ring. A wide variety of cyclic ketones have been allowed to react in this way. For instance, the enamine (75) gave 76 on reaction with dimethyl acetylenedicarboxylate in refluxing toluene (55) and the heterocyclic enamine (77) obtained from dihydro-3-(2H)-... 

A two-carbon ring expansion of cyclic ketones was achieved by the addition of acetylenic esters and diesters to the enamine derivatives of the ketones, and reported almost simultaneously from several laboratories (337-343). The intermediate bicyclic adduct could be isolated in some cases. 

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