6-membered

Both quaternary nitrogen and pyridine have a 6-membered ring structure.

It is interesting to note that 1,1-CBDCA has a higher stability constant than that of malonic acid, although both form 6-membered chelate rings.

The third generation of 2',4'-BNA-NC contains a 6-membered ring with a N-O bond between the 2'-hydroxyl and the 4'-carbon of the ribose moiety.

They differ in that the 5-membered thiazolidine ring of penicillin is replaced in the cephalosporins with a 6-membered dihydrothiazine ring.

This has led to the postulate of a 6-membered complex with coordination of [Mn.sup.+] to both S and N, which increases the electrophilic character of P and thereby makes degradation via nucleophilic attack by O[H.sup.-]/[H.sub.2]O more energetically favourable.

11) Group G C[H.sub.3] Single-bonded 214 C[H.sub.2] 133 CH< 28 >C< -93 C[H.sub.2]= Double bonded 190 -CH= 111 >CH= 19 -CH=C< 285 >C=C< 222 Phenyl 735 Phenylene o,m,p 658 Napthenyl 1,146 Ring 5-membered 105-115 Ring 6-membered 95-105 Conjugation 20-30 H Variable 80-100 O Ethers 70 CO Ketones 275 COO Esters 310 CN 410 CI Mean 260 CI Single 270 CI Twin (>CC[I.sub.2]) 260 CI Triple (-(CC[I.sub.3]) 250 Br Single 340 I Single 425 C[F.sub.2] n-fluorocarbons 150 C[F.sub.3] 274 S Sulfides 225 SH Thiols 315 ONO Nitrates ~440 N[0.sub.2] Nitro-compounds ~440 P[0.sub.4] Organic phosphates ~500 -38 Table 2--solubility parameters for common polymers (ref.

Ichikawa, "Fluorinated isoquinolines: synthesis, properties and applications," in Fluorine in Heterocyclic Chemistry Volume 2: 6-Membered Heterocycles, V.

Variation of N-substitution at the 6-membered ring will result in additional advantages for biological applications.

Good enantiomeric excess was attained for 6-membered ring lactams in the presence of a chiral ligand.