It appears there may be a misunderstanding in your question regarding hydrogen bonding and aromatic substitution. The terms "para directing" and "hydrogen bonding" refer to different concepts in chemistry.
1. Para Directing Groups: In the context of electrophilic aromatic substitution, substituents on a benzene ring can influence the position where new substituents are added. Substituents can be classified as ortho/para-directing or meta-directing based on how they affect the electron density of the aromatic ring. Ortho/para-directing groups are typically electron-donating groups, such as -OH, -OCH3, and -NH2. In contrast, meta-directing groups are typically electron-withdrawing groups, such as -NO2 and -COOH.
2. Hydrogen Bonding: Hydrogen bonding is a specific type of intermolecular force that occurs between molecules or within different parts of a single molecule due to the attraction between a hydrogen atom that is covalently bonded to a highly electronegative atom (such as O, N, or F) and another electronegative atom.
To clarify, the notion of hydrogen bonding is unrelated to whether a substituent is para directing or otherwise. Para directing does not imply a lack of hydrogen bonding. Instead, whether hydrogen bonding occurs depends on the presence of suitable hydrogen bond donors (hydrogens attached to electronegative atoms) and acceptors (electronegative atoms with lone pairs).
Summary
- The classification of substituents as para directing is about their influence on electrophilic aromatic substitution reactions—not about hydrogen bonding.
- Hydrogen bonding involves specific interactions and is unrelated to the directing effects of substituents on a benzene ring.
If you have specific examples or contexts in mind concerning para directing groups and hydrogen bonding, please share, and I can provide a more tailored explanation!