The ionic nature of a compound can be assessed by comparing its observed dipole moment to the theoretical dipole moment it would have if the bond were 100% ionic. According to the sources, the dipole moment ($\mu$) is defined as the product of the magnitude of charge ($Q$) and the distance of separation ($r$), so $\mu = Q \times r$ . The percentage ionic character is proportional to the ratio of the dipole moment to the bond length ($\mu/r$).

1. For compound AB: The ratio is $\frac{10.92}{2.72} \approx 4.015$ D/$\text{\AA}$.
2. For compound CD: The ratio is $\frac{12.45}{2.56} \approx 4.863$ D/$\text{\AA}$.

Comparing these values, the ratio for compound CD is significantly higher than that for AB. This indicates that for a given bond length, CD has a greater magnitude of charge separation, reflecting a higher percentage of ionic character. Therefore, compound CD exhibits more ionic nature.