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How LLMs Could Change AI Reaction Prediction and Synthesis Planning

LLMs are entering chemistry systems for route search, reaction prediction and experimental workflows, often alongside specialist models and tools. Their published scores measure different tasks, not a universal ability to plan or run a successful synthesis.
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Large language models (LLMs) are changing how researchers build AI tools for chemistry—but they have not made specialist reaction-prediction systems, synthesis-planning software, or chemists obsolete. The strongest current work combines language models with structured chemical data, search algorithms, databases, and, in some demonstrations, laboratory automation. What these systems can do depends on the task: predicting a reaction product, planning a route backward from a target molecule, and developing and running an experiment are different capabilities.

What does it mean for AI to predict a reaction or plan a synthesis?

These phrases describe related but distinct jobs. A result on one job does not establish that a system can do the others.

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  • Reaction prediction estimates products from reactants and reaction conditions. Some systems instead work backward from a product representation to likely reactants for a single transformation.
  • Retrosynthesis starts with a desired molecule and searches backward for candidate precursors and a sequence of transformations that could lead to it.
  • Reaction development and execution goes beyond proposing a route: it can include finding relevant literature, selecting and testing conditions, analyzing results, and adjusting the experiment.

LLMs can contribute chemical language understanding, literature handling, or reasoning across steps. But a useful chemistry system may also depend on reaction representations, specialist models, search methods, databases, and experimental tools. Calling all of these tasks “AI chemistry” obscures the difference between a plausible suggestion and a route that has been made to work.

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How LLMs are changing synthesis planning

Searching routes rather than predicting one step at a time

A 2025 ICML paper explores LLM-augmented, route-level search for multistep retrosynthesis. The authors describe encoding reaction pathways and searching routes beyond conventional step-by-step reactant prediction. This is a different planning strategy: rather than treating a synthesis solely as a chain of isolated predictions, the system searches across candidate pathways. The paper is evidence for that approach, not proof that an LLM alone can reliably select an executable route.

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Generating retrosynthetic proposals with a trained transformer

A 2025 Nature Communications paper presents RSGPT, a generative transformer pretrained on generated reaction data for retrosynthesis. Its abstract reports 63.4% Top-1 accuracy on the paper’s benchmark. That figure describes the benchmark result—not the percentage of proposed syntheses that succeed in a laboratory, and not a general success rate for AI planning.

Combining chemical reasoning with traditional search

A 2026 Matter paper describes a system integrating LLM chemical reasoning with traditional search algorithms for strategy-aware synthesis planning and reaction-mechanism elucidation. The publisher’s research highlights report 71% alignment with independent expert chemists for the study’s evaluation. That is an expert-alignment result under the paper’s evaluation, not a universal accuracy rate or confirmation that every suggested route is experimentally feasible.

Can an LLM help develop and run experiments?

Some research connects language-model components to a broader experimental workflow. A 2024 Nature Communications paper describes an LLM-based reaction-development framework with six specialized agents:

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  • Literature Scouter
  • Experiment Designer
  • Hardware Executor
  • Spectrum Analyzer
  • Separation Instructor
  • Result Interpreter

The authors describe a copper/TEMPO-catalyzed aerobic alcohol oxidation workflow that included literature search, condition screening, kinetics, optimization, scale-up, and purification. They also report work on three other reaction types. This demonstrates an integrated research workflow, not that all stages can be safely or independently automated in an ordinary laboratory. A system’s proposed experiment still needs to be assessed for the relevant chemicals, equipment, hazards, and operating procedures.

What the reported performance numbers do—and do not—show

Published figures for these systems cannot be combined into a single ranking: the studies address different chemical domains and tasks and use different evaluation designs and metrics.

Study and domain Task or approach Reported result How to interpret it
ICML, 2025; retrosynthesis LLM-augmented route-level search over multistep pathways No headline performance figure stated in the cited study description Evidence for a route-search strategy, not a general laboratory-success measure.
Nature Communications, 2025; retrosynthesis RSGPT generative transformer pretrained on generated reaction data 63.4% Top-1 accuracy on the paper’s benchmark A benchmark result, not an experimental success rate.
Matter, 2026; synthesis planning and mechanism elucidation LLM chemical reasoning integrated with traditional search 71% alignment with independent expert chemists, as reported in the publisher’s research highlights An evaluation-specific expert-alignment result, not universal accuracy.
ACS Applied Materials & Interfaces, 2025; inorganic materials Precursor and temperature prediction for inorganic synthesis On 1,000 held-out reactions, up to 53.8% Top-1 precursor accuracy and 66.8% Top-5 performance; mean absolute errors below 126 °C for calcination and sintering temperature predictions Study-specific results for inorganic synthesis. They should not be transferred to organic reaction prediction or treated as representative of every model.

Even within a single study, a metric only answers the question its evaluation measures. Top-1 accuracy asks whether the first prediction matches the benchmark target; Top-5 asks whether the target appears among five candidates. Neither by itself tests selectivity, practical conditions, safety, reproducibility, or whether a proposed multistep route works at the bench. Expert agreement is a different kind of measure again.

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What still needs checking before a proposed route is useful?

A chemically plausible answer is a starting point, not an experimental result. For a particular synthesis, the proposal has to be judged in its chemical and laboratory context. Relevant checks include:

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  • Route feasibility: whether the proposed transformations and precursors make sense for the target and the available starting materials.
  • Selectivity and conditions: whether the expected product can be favored under conditions that are established or can be tested.
  • Safety and equipment: whether reagents, temperatures, pressures, and operations are appropriate for the lab and its controls.
  • Evidence and reproducibility: whether literature precedent or experimental measurements support the steps, and whether another run can reproduce the result.

A route-search output, a reaction benchmark score, and a completed automated workflow answer different questions. When evaluating a chemistry AI claim, check the chemical domain, task, benchmark or experimental setup, metric, use of external tools, and whether the proposed results were experimentally verified.

What this means for chemists and chemistry software

The important shift is architectural: LLMs are being tested as reasoning components inside systems that can search routes, consult chemical information, or coordinate specialized tasks. That may make tools more flexible than a single model devoted to one prediction task. It does not establish that a general-purpose chatbot can replace specialist chemistry software or expert judgment.

A 2023 Nature article on autonomous chemical research mentions reaction databases such as Reaxys and SciFinder as resources that could enhance multistep synthesis planning. That observation does not establish current integrations or partner arrangements. More broadly, access to literature or reaction data can help a planning system, but it does not itself validate a route.

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