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Ingredients such as polyphosphate, zinc salts, and chlorhexidine have active properties to help prevent or reduce the formation of plaque and tartar. [13] [15] These compounds are able to work on the whole mouth including between teeth and all the way up to the gum line, and is not limited to just the chewing contact surface area. [14]
Pyrylium's electrophilicity makes them useful materials for producing other compounds with stronger aromatic character. Pyrylium salts afford pyridines with ammonia, [16] pyridinium salts with primary amines, pyridine-N-oxides with hydroxylamine, phosphabenzenes with phosphine derivatives, thiopyrylium salts with hydrogen sulfide, and benzene ...
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This difference is partly related to the lower symmetry of the individual pyridine molecule (C 2v vs D 6h for benzene). A trihydrate (pyridine·3H 2 O) is known; it also crystallizes in an orthorhombic system in the space group Pbca, lattice parameters a = 1244 pm, b = 1783 pm, c = 679 pm and eight formula units per unit cell (measured at 223 K).
For example, the aromatic species 1 can be reduced to 2 with a relatively small penalty for forming an antiaromatic system. The antiaromatic 2 does revert to the aromatic species 1 over time by reacting with oxygen in the air because the aromaticity is preferred. [15] The loss of antiaromaticity can sometimes be the driving force of a reaction.
The lowest triplet state of an annulene is, according to Baird's rule, aromatic when it has 4n π-electrons and antiaromatic when the π-electron count is 4n + 2, where n is any positive integer. This trend is opposite to that predicted by Hückel's rule for the ground state, which is usually the lowest singlet state (S 0).
Hückel's rule can also be applied to molecules containing other atoms such as nitrogen or oxygen. For example pyridine (C 5 H 5 N) has a ring structure similar to benzene, except that one -CH- group is replaced by a nitrogen atom with no hydrogen. There are still six π electrons and the pyridine molecule is also aromatic and known for its ...
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