does it make any difference writing NO2 instead of O2N
The Graphical Representation Standards for Chemical Structure Diagrams (IUPAC Recommendations 2008), include recommendations for contracted labels in structure diagrams. In particular


  GR-2.3.1 General guidelines
  Atom labels representing more than one non-hydrogen atom—also sometimes known as “contracted” labels—rely on the fact that many elements have consistent and well-understood bonding patterns. (…)


 


  GR-2.3.3 Orientation of symbols within contracted labels
  Contracted atom labels attached to only one bond should be read outwards from that bond, usually from left to right if the bond is on the left of the label. If the bond is instead attached to the right of the label, the label will normally be read from right to left, but ambiguities can result. Accordingly, contracted labels with a bond on the right should be avoided except for simple cases, usually limited to relatively small labels containing four or fewer combined element symbols and abbreviations. (…)


 


  GR-2.3.4 Interpretation of contracted labels
  In general, contracted labels are interpreted to fill as many valences as possible, as quickly as possible. (…)


Contracted labels for nitro groups cannot be interpreted with a simple application of valence rules, but also need some implicit charges to be added. It is equally possible to avoid entirely the issue of depiction and instead display the functional group using the $\ce{NO2}$ abbreviation. According to Table III in the Graphical Representation Standards, the left-to-right form of the label is $\ce{-NO2}$ and the corresponding right-to-left form is $\ce{O2N-{}}$.