3 years ago

A Critical Check for the Role of Resonance in Intramolecular Hydrogen Bonding

A Critical Check for the Role of Resonance in Intramolecular Hydrogen Bonding
Wei Wu, Yirong Mo, Huaiyu Zhang, Xiaoyu Jiang
Although resonance-assisted H-bonds (RAHBs) are well recognized, the role of π resonance in RAHBs is controversial, as the seemingly enhanced H-bonds in unsaturated compounds may result from the constraints imposed by the σ skeleton. Herein the block-localized wave function (BLW) method, which can derive optimal yet resonance-quenched structures with related physiochemical properties, was employed to examine the correlation between π resonance and the strength of intramolecular RAHBs. Examination of a series of paradigmatic molecules with RAHBs and their saturated analogues showed that it is inappropriate to compare a conjugated system with its saturated counterpart, as they may have quite different σ frameworks. Nevertheless, comparison between a conjugated system and its resonance-quenched (i.e., electron-localized) state, which have identical σ skeletons, shows that in all studied cases, π resonance unanimously reduces the bonding distance by 0.111–0.477 Å, strengthens the bonding by 40–56 %, and redshifts the D−H vibrational frequency by 104–628 cm−1. Furthermore, there is an excellent correlation between hydrogen-bonding strength and the classical Coulomb attraction between the hydrogen-bond donor and the acceptor, which suggests that the dominant role of the electrostatic interaction in H-bonds and RAHBs originates from the charge flow from H-bond donors to acceptors through π conjugation. On and off: The block-localized wave function method can theoretically switch off the resonance effect and examine the correlation between π resonance and the strength of an intramolecular resonance-assisted H-bond (RAHB, see figure). Indeed, π resonance significantly reduces the bonding distance, strengthens the bonding, and redshifts the DH vibrational frequency, and this confirms that the RAHB origins from the charge flow from the H-bond donor (D) to the acceptor through the π conjugation.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201703952

You might also like
Discover & Discuss Important Research

Keeping up-to-date with research can feel impossible, with papers being published faster than you'll ever be able to read them. That's where Researcher comes in: we're simplifying discovery and making important discussions happen. With over 19,000 sources, including peer-reviewed journals, preprints, blogs, universities, podcasts and Live events across 10 research areas, you'll never miss what's important to you. It's like social media, but better. Oh, and we should mention - it's free.

  • Download from Google Play
  • Download from App Store
  • Download from AppInChina

Researcher displays publicly available abstracts and doesn’t host any full article content. If the content is open access, we will direct clicks from the abstracts to the publisher website and display the PDF copy on our platform. Clicks to view the full text will be directed to the publisher website, where only users with subscriptions or access through their institution are able to view the full article.