Unlocking‐alk‐1‐ynes conformers: Quantum “trigger finger” versus “stiff joint” conformations
Source: PubMed Central Open Access, NCBI / U.S. National Library of Medicine
Abstract Molecular conformation in‐alk‐1‐ynes (CnA) is conventionally simplified to an all‐planar structure. We report a comprehensive quantum chemical analysis revealing two near‐isoenergetic rotamers at the acetylenic terminus: planar () and skewed (). The high, symmetric rotational energy barrier (meV) arises from unique steric relief near thecenter coupled with electronic stabilization of. This creates a unique kinetic profile: a Quantum “Trigger Finger” (rotation) that enforces anensemble, sharply contrasting with the thermodynamically biased “Stiff Joint” (rotation) of the alkyl chain. This structural degeneracy necessitates ensemble averaging for spectroscopic data interpretation, while the slow interconversion permits kinetic trapping and intentional conformer enrichment during synthesis and molecular junction fabrication. Our work redefines the alkyne anchor, providing a blueprint for accurate interpretation of spectroscopic data and achieving conformational control in molecular electronics. Quantum chemical analysis reveals the unique function of‐alk‐1‐yne terminus as a Quantum “Trigger Finger,” exhibiting two near‐isoenergetic conformers ( and ) locked by a symmetric high barrier. This contrasts with the lower asymmetric barrier of the conventional asymmetric “Stiff Joint” alkyl chain. The resulting 50%:50% ensemble is key for spectroscopy, yet permits kinetic trapping for predictable molecular junction fabrication. C s http://www.w3.org/1998/Math/MathML jats-math-
Abstract
Abstract Molecular conformation in‐alk‐1‐ynes (CnA) is conventionally simplified to an all‐planar structure. We report a comprehensive quantum chemical analysis revealing two near‐isoenergetic rotamers at the acetylenic terminus: planar () and skewed (). The high, symmetric rotational energy barrier (meV) arises from unique steric relief near thecenter coupled with electronic stabilization of. This creates a unique kinetic profile: a Quantum “Trigger Finger” (rotation) that enforces anensemble, sharply contrasting with the thermodynamically biased “Stiff Joint” (rotation) of the alkyl chain. This structural degeneracy necessitates ensemble averaging for spectroscopic data interpretation, while the slow interconversion permits kinetic trapping and intentional conformer enrichment during synthesis and molecular junction fabrication. Our work redefines the alkyne anchor, providing a blueprint for accurate interpretation of spectroscopic data and achieving conformational control in molecular electronics. Quantum chemical analysis reveals the unique function of‐alk‐1‐yne terminus as a Quantum “Trigger Finger,” exhibiting two near‐isoenergetic conformers ( and ) locked by a symmetric high barrier. This contrasts with the lower asymmetric barrier of the conventional asymmetric “Stiff Joint” alkyl chain. The resulting 50%:50% ensemble is key for spectroscopy, yet permits kinetic trapping for predictable molecular junction fabrication. C s http://www.w3.org/1998/Math/MathML jats-math-9 inline C 1 http://www.w3.org/1998/Math/MathML jats-math-10 inline ≈ http://www.w3.org/1998/Math/MathML jats-math-11 inline http://www.w3.org/1999/xlink anchor jats-graphic-1 portrait SMO2-9999-0-g003.jpg anchor graphic portrait graphical