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I have provided two images to help with this question. The first image is the reaction that is taking place. The γ-pyran is treated with the hydride acceptor triphenylmethyl perchlorate. A hydride is a hydrogen atom containing a lone pair of electrons giving it a negative charge. The triphenylmethyl cation is a positively charged carbocation that greatly wants to accept an electron pair to stabilize its charge. Therefore, it abstracts a hydride from the γ-puran starting material. It grabs one of the hydrogen atoms that is drawn in the reaction scheme. This results in the formation of triphenylmethane and a pyrylium perchlorate salt with the formula C₅H₅ClO₅. The important aspect of the structure is shown in the attached images. The most stable resonance form of the pyrylium cation is shown with a positive charge on the oxygen.
The reason this pyrylium ion is the most stable resonance form is because the formation of the oxonium ion (positive charged oxygen with 3 bonds) leads to an aromatic compound. There are 6 pi electrons in conjugation in this ring similar to a benzene ring and this results in the most stable structure.
The reason this pyrylium ion is the most stable resonance form is because the formation of the oxonium ion (positive charged oxygen with 3 bonds) leads to an aromatic compound. There are 6 pi electrons in conjugation in this ring similar to a benzene ring and this results in the most stable structure.