In non-polar hexane, the dominant species of pentane-2,4-dione is

In non-polar media the enol with an intramolecular $\mathrm{O}-\mathrm{H}\cdot \cdot \cdot \mathrm{O}$ hydrogen bond (six-membered chelate) is strongly favoured and amounts to about 97 percent. Only the Z (cis) enol can form the chelate. The E enol cannot, and the terminal enol $\mathrm{CH}{}_2=\mathrm{C}(\mathrm{OH})\mathrm{CH}{}_2\mathrm{COCH}{}_3$ lacks conjugation, so both are minor.