difference in boiling point of 2-iodopentane and 3-iodopentane
I have spent a quite a time to figure out "so-called" irrational behavior of the boiling points of iodoalkanes compared to relevent othe halpalkane, but I have seen noting really radical, what OP claimed there are. The following chart listed boiling points of all possible long chain halides of pentane (all have been measured at $\pu{760 mmHg}$):
$$
\begin{array}{ccc}
\text{locant} &amp;\text{fluoropentane} &amp; \text{chlororopentane} &amp; \text{bromoropentane} &amp; \text{iodopentane}\\\hline
1 &amp; \pu{62.8 ^\circ C} &amp; \pu{108 ^\circ C} &amp; \pu{130 ^\circ C} &amp; \pu{155 ^\circ C}\\
2 &amp; \pu{58.4 ^\circ C} &amp; \pu{99 ^\circ C} &amp; \pu{117 ^\circ C} &amp; \pu{150 ^\circ C}\\
3 &amp; \pu{59.5 ^\circ C} &amp; \pu{97.5 ^\circ C} &amp; \pu{119 ^\circ C} &amp; \pu{145 ^\circ C}\\
\end{array}
$$

Please be aware that, all of these values are extracted from EPA(USA) website. Also note that values of 2-fluoropentane and 3-fluoropentane are predicted on EPA, but ChemSpider gave experimental values of $\pu{56 ^\circ C}$ and $\pu{56.7 ^\circ C}$, respectively. Also, the boiling point of 3-iodopentane ($\pu{145 ^\circ C}$) has also been predicted, but it is available commercially at Alfa Aesar, which listed the boiling point of it as $\pu{146.6 ^\circ C}$. Thus, these listed values are very reliable. Therefore, I'd say that the values OP has must be not so reliable. I admit that I have to dig deeper to find a reliable source of those predicted values. All three bromo compounds have no problem because all of them are available in Sigma-Aldrich.