Grounding Structure in Language: Enriching Symbolic Representations for Molecular Reasoning

Zhengyuan Liu, Dan He, Nancy F. Chen, Wenya Wang


Abstract
Large language models (LLMs) show promise for scientific applications but struggle when domain knowledge is encoded in complex structures. Chemistry exemplifies this challenge: molecular structures encode rich relational data that dictates chemical meaning, yet standard formats like SMILES obscure this through arbitrary linearization. In this work, we systematically characterize which structural information lost during linearization most severely hampers LLM reasoning, decomposing the problem into IUPAC-grounded dimensions: substituent positions (locants), attachment points (anchoring), and modification constraints (valency). Our diagnostic reveals non-uniform failures across dimensions, with locant identification being especially challenging. We directly address the failures by grounding the linearized representations in structural context with each component targeting its corresponding diagnostic dimension. General-purpose LLMs with explicit grounding can outperform chemistry-specialized models on structure-aware molecule manipulation, suggesting structural context can compensate for domain-specific training. Moreover, we investigate a training-free inductive protocol that nearly doubles the accuracy of weaker models. These results point toward explicit structural grounding as a principled path to more reliable molecular reasoning across model scales.
Anthology ID:
2026.findings-emnlp.819
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
Findings
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SIGDAT
Publisher:
Association for Computational Linguistics
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Pages:
17362–17382
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URL:
https://aclanthology.org/2026.findings-emnlp.819/
DOI:
Bibkey:
Cite (ACL):
Zhengyuan Liu, Dan He, Nancy F. Chen, and Wenya Wang. 2026. Grounding Structure in Language: Enriching Symbolic Representations for Molecular Reasoning. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 17362–17382, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Grounding Structure in Language: Enriching Symbolic Representations for Molecular Reasoning (Liu et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-emnlp.819.pdf