In Memoriam: Professor Yitzhak Apeloig, President and Distinguised Professor of the Technion
Reporters: Aviva Lev-Ari, PhD, RN and Stephen J. Williams, Ph.D.
From the Technion:
Distinguished Professor Yitzhak Apeloig (1944–2026), president of the Technion from 2001 to 2009 and one of Israel’s most distinguished chemists
A brief synopsis of Dr. Apeloig’s scientific achievements and contributions toward the field of chemistry:
1. Pioneering Computational Quantum Chemistry
In the 1970s, Apeloig was one of the first experimental chemists in the world to recognize the immense potential of using quantum theory and computational models to predict molecular characteristics.
- The “First Calculate, Then Synthesize” Philosophy: He pioneered a paradigm shift in organic chemistry by using quantum-mechanical calculations to predict whether a novel molecule could exist and what its lifespan would be before attempting physical synthesis in the laboratory.
- He was unique for his time in requiring his students to master both computational modeling and physical laboratory experimentation rather than separating the disciplines.
2. Breakthroughs in Organosilicon Chemistry
Before Apeloig’s work, much of the scientific community believed that silicon could not easily form stable multiple bonds (such as $Si=Si$ or $Si=C$ double bonds) in the way carbon does. Apeloig revolutionized the field of organosilicon chemistry:
- Low-Coordination Silicon Compounds: He successfully used computational tools combined with experimental testing to predict, isolate, and understand highly reactive, low-coordination silicon species. This included landmark research into multiply-bonded silicon compounds, silyl radicals, silyl anions, silylenes, and metallosilane reagents.
- Silicone and Materials Science: His structural insights fundamentally advanced the molecular understanding of silicon polymers and siloxanes, which heavily influenced the development of advanced moulding materials, rubbers, and photosensitive materials used in lithography.
3. Discovery of Reactive Intermediates
During his early career and PhD research, he focused heavily on physical organic chemistry and organic reaction mechanisms:
- He was the first to experimentally demonstrate that a vinyl cation holds a linear geometry around its carbocationic center.
- His extensive work mapping out short-lived, highly reactive intermediates (like carbenium ions and strained molecules) provided the foundational mechanics for how complex organic reactions occur.
Major Recognitions
For these definitive contributions to computational and silicon chemistry, Apeloig was awarded some of the highest honors in the discipline:
- The Schrödinger Medal (2021): Awarded by the World Association of Theoretical and Computational Chemists (WATOC) for his seminal contributions to theoretical chemistry.
- The ACS Frederic Stanley Kipping Award in Silicon Chemistry (2010): The premier international award recognizing advancements in the study of silicon.
- The Wacker Silicone Award (2007) and the Israel Chemical Society Gold Medal (2017).
The seminal publications that define his academic footprint include:
1. Foundational Computational and Structural Chemistry
During the mid-1970s and 1980s, Apeloig co-authored several massive, highly cited studies establishing the rules of computational molecular architecture, specifically challenging traditional rules of carbon and silicon bonding.
- “Stabilization of planar tetracoordinate carbon”
- Journal of the American Chemical Society (1976)
- Co-authors: J. B. Collins, J. D. Dill, E. D. Jemmis, P. v. R. Schleyer, R. Seeger, J. A. Pople
- Impact: A true milestone in structural chemistry that theoretically demonstrated how specific substitution patterns could stabilize a planar geometry around a carbon atom, defying the standard tetrahedral configuration.
- “A theoretical survey of unsaturated or multiply bonded and divalent silicon compounds. Comparison with carbon analogs”
- Journal of the American Chemical Society (1986)
- Co-authors: B. T. Luke, J. A. Pople, M. B. Krogh-Jespersen, M. Karni, J. Chandrasekhar, P. v. R. Schleyer
- Impact: A definitive ab initio survey that comprehensively mapped out the differences between carbon and silicon multiple bonds, predicting the stability and reaction behaviors of transient silicon chemical species.
2. High-Impact Silicon and Stable Carbene Analogs
In the 1990s and 2000s, Apeloig focused on predicting and identifying highly sought-after reactive intermediates—particularly “impossible” double bonds and carbenes.
- “On the Question of Stability, Conjugation, and ‘Aromaticity’ in Imidazol-2-ylidenes and Their Silicon Analogs”
- Journal of the American Chemical Society (1996)
- Co-authors: C. Heinemann, T. Müller, H. Schwarz
- Impact: Heavily cited paper evaluating the electronic properties, structural stability, and aromaticity of N-heterocyclic carbenes (NHCs) versus their heavier silicon counterparts (silylenes).
- “Substituent effects on the geometries and energies of the silicon-silicon double bond”
- Journal of the American Chemical Society (1990)
- Co-author: M. Karni
- Impact: This study mapped how changing the attached chemical groups altered the trans-bending and bond lengths of $Si=Si$ double bonds, establishing a predictive guide for experimentalists trying to isolate stable disilenes.
3. Definitive Academic Reviews and Reference Books
Beyond standalone journal entries, Apeloig is globally recognized for editing the foundational texts that summarized the state of organosilicon chemistry for generations of scientists.
- “The Chemistry of Organic Silicon Compounds” (Volumes 1, 2, and 3)
- Co-edited with: Zvi Rappoport (Published by John Wiley & Sons, beginning in 1989)
- Impact: Apeloig authored critical chapters, such as “Theoretical Aspects of Organosilicon Compounds,” within these volumes. This multi-book compendium serves as the literal “bible” for researchers studying silicon polymers, reactive silicon intermediates, and silicon-based material sciences.
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A pioneer in computational chemistry and organosilicon compounds, Prof. Apeloig made groundbreaking scientific contributions while mentoring generations of researchers and helping position the Technion as a global leader in science and technology.
During his presidency, he expanded interdisciplinary research, strengthened international partnerships, increased investment in research infrastructure and scholarships, and advanced collaboration between engineering, medicine, and the humanities.“Prof. Apeloig led the Technion with quiet confidence and steadfast leadership,” said Technion President Prof. Uri Sivan. “His years in office were marked by exceptional academic development and a profound impact on the State of Israel and beyond.”
The Technion was his home and family. He will be deeply missed. May his memory be a blessing.