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p-Xylene
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<p><i>p</i>-Xylene (<a href="/facts/Arene_substitution_pattern/ByM7Y1b9"><i>para</i></a>-xylene) is an <a href="/facts/Aromatic_hydrocarbon/3EXq8Tgf">aromatic hydrocarbon</a>. It is one of the three <a href="/facts/Isomer/PXlvDVdg">isomers</a> of <a href="/facts/Xylene/BEGggD9s">dimethylbenzene</a> known collectively as <a href="/facts/Xylene/BEGggD9s">xylenes</a>. The <i>p-</i> stands for <i>para-</i>, indicating that the two methyl groups in <i>p</i>-xylene occupy the diametrically opposite substituent positions 1 and 4. It is in the positions of the two methyl groups, their <a href="/facts/Arene_substitution_pattern/ByM7Y1b9">arene substitution pattern</a>, that it differs from the other isomers, <a href="/facts/O-Xylene/lCELfssz"><i>o</i>-xylene</a> and <a href="/facts/M-Xylene/R18IDFIS"><i>m</i>-xylene</a>. All have the same chemical formula C6H4(CH3)2. All xylene isomers are colorless and highly flammable. The odor threshold of <i>p</i>-xylene is 0.62 <a href="/facts/Parts_per_million/PozRuoLM">parts per million</a> (ppm). </p>