Naphtha boiling range compositions are provided that can have improved combustion properties (relative to the research octane number of the composition) in spark ignition engines and/or compression ignition engines. The improved combustion properties can be achieved by controlling the total combined amounts of n-paraffins and isoparaffins that include a straight-chain propyl group (R.sub.1CH.sub.2CH.sub.2CH.sub.2R.sub.2). For such a straight-chain propyl group, R.sub.2 can correspond to any convenient C.sub.xH.sub.y group that can appear in a paraffin or isoparaffin. R.sub.1 can correspond to a hydrogen atom, making the straight-chain propyl group a terminal n-propyl group; or R.sub.1 can correspond to any convenient C.sub.xH.sub.y group that can appear in a paraffin or isoparaffin.

Aviation gasolines and additives may have manganese-containing anti-knock components. The scavengers herein mitigate the possible deleterious effects from using the manganese-containing anti-knock. The scavengers include molecules with a central atom of a Group 15 element other than nitrogen. Entities that are attached to the central atom are electron withdrawing entities including electron deficient atoms and electron deficient functional groups.