The Nature and Analysis of Substituent Electronic Effects

Topsom, R. D.

doi:10.1002/9780470171912.ch1

Cited by 139 publications

(8 citation statements)

References 54 publications

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“…Charge redistribution due to functional substituents is common in organic compounds, including the substituent effect in saturated chains or aromatic rings. − This effect is also observed for AgSC n by 13 C NMR in this work.…”

Section: Discussionsupporting

confidence: 68%

Critical Size for Bulk-to-Discrete Transition in 2D Aliphatic Layers: Abrupt Size Effect Observed via Calorimetry and Solid-State ¹³C NMR

Rama

Efremov

et al. 2017

J. Phys. Chem. C

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Anomalous changes of physical properties are observed in an abrupt bulk-to-discrete transition in layered silver alkanethiolate (AgSCn, n = 1–16). A critical chain length of n cr = 7 marks the sharp boundary between the bulk (uniform, n ≥ 7) and discrete (individualistic, n ≤ 6) forms of AgSCn. Solid-state 13C NMR analysis reveals that none of the carbons share identical chemical environment in the discrete range, making each AgSCn with n = 2–6 uniquely different material, even though the crystal structure is preserved throughout. Extraordinary changes of thermodynamic properties appearing at this bulk-to-discrete transition include ∼500% increases of melting enthalpy (ΔH m), ∼50 °C increases of melting point (T m), and an atypical transition between size-dependent T m depression and T m enhancement. We develop a new comprehensive Gibbs–Thomson model with piecewise excess free energy (ΔG excess) to predict the nature of the abrupt size effect melting. A new 3D spatial model is constructed to divide the aliphatic chains of AgSCn into three bulk or discrete segments: (a) tail segment containing three carbons, (b) head segment containing two carbons, and (c) bulk mid-chain segment containing (n – 5) carbons. Odd/even effect of T m and ΔH m is described by a constant ΔG excess over the entire chain length range of AgSCn and is exclusively attributed to the localized tail segment. Bulk-to-discrete transition occurs when material properties are dominated by the discrete head and tail segments at n < n cr. Values of n cr are independently measured by both calorimetry and 13C NMR. This analysis is generalized to other aliphatic layers including n-alkanes with n cr ≈ 11. This work is seminal to the design of novel aliphatic layers with tailorable properties (e.g., T m) and has applications in molecular electronics and biophysics.

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Section: Discussionsupporting

confidence: 68%

Critical Size for Bulk-to-Discrete Transition in 2D Aliphatic Layers: Abrupt Size Effect Observed via Calorimetry and Solid-State ¹³C NMR

Rama

Efremov

et al. 2017

J. Phys. Chem. C

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“…Central to the Chemist’s intuition for designing molecules with desirable properties, the effects of substituents on the π- and σ-orbital systems are well-described empirically. , Logically similar chemical intuition for tuning QI ought to exist. Indeed, Andrews et al demonstrated that a class of cross-conjugated molecules follows simple substituent rules: The antiresonance energy is lowered by electron acceptors and raised by electron donors.…”

Section: Introductionmentioning

confidence: 99%

Tuning Conductance in Aromatic Molecules: Constructive and Counteractive Substituent Effects

2016

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Destructive quantum interference in aromatic hydrocarbons can be tuned using chemical substituents; however, classical chemical intuition is not enough to explain the effects on electron transport. Using Hückel theory and density functional theory calculations, in combination with the Landauer–Büttiker approach for charge transport, novel substituent effects are demonstrated. For a 1,3-linked benzene, an electron acceptor in position 2 is shown to have the same effect on the antiresonance energy as an electron donor in position 4 and vice versa. Substituents in position 5 have no effect on the antiresonance energy. The effects appear to be additive, such that a donor in position 2 will counteract a donor in position 4, leading to cancellation of the substituent effect. Counter- and nonactive substituent positions exist for all aromatic hydrocarbons and can be predicted using a diagrammatic approach. This insight should be useful when substituents are to be used for tuning destructive quantum interference features in the transmission relative to the Fermi energy of the electrodes.

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“…Energetic considerations and traditional models involving ''resonance effects'' and alternating charge accumulation along atoms of aromatic rings have provided attractive, although somewhat simplistic theoretical explanations for the interpretation of such substituent effects. [1][2][3][4][5] These early advances 5 have been followed by a large number of more detailed studies involving various quantum chemistry methods. In this context, besides the computational methodology advances which have made possible a more rigorous basis for interpretation, the approaches to a quantum-chemical analysis of molecular similarity, suitable for numerically evaluating even small variations in intramolecular effects, have provided an important framework.…”

Section: Introductionmentioning

confidence: 99%

Substituent effects and local molecular shape correlations

Antal

Mezey

2014

Phys. Chem. Chem. Phys.

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Using a detailed electron density shape analysis methodology, a new method is proposed for studying the main components of substituent effects in a series of disubstituted benzenes, in correlation with their activating and deactivating characteristics as observed by the induced shape changes of a local electron density cloud. The numerical measures obtained for the extent of shape changes can be correlated with known and with some unexpected effects of various substituents. The insight obtained from the shape analysis provides a theoretical, electron density based justification for some well-known trends, but it also provides new explanations for some of the unexpected features of these substituent effects.

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The Nature and Analysis of Substituent Electronic Effects

Cited by 139 publications

References 54 publications

Critical Size for Bulk-to-Discrete Transition in 2D Aliphatic Layers: Abrupt Size Effect Observed via Calorimetry and Solid-State ¹³C NMR

Critical Size for Bulk-to-Discrete Transition in 2D Aliphatic Layers: Abrupt Size Effect Observed via Calorimetry and Solid-State ¹³C NMR

Tuning Conductance in Aromatic Molecules: Constructive and Counteractive Substituent Effects

Substituent effects and local molecular shape correlations

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The Nature and Analysis of Substituent Electronic Effects

Cited by 139 publications

References 54 publications

Critical Size for Bulk-to-Discrete Transition in 2D Aliphatic Layers: Abrupt Size Effect Observed via Calorimetry and Solid-State 13C NMR

Critical Size for Bulk-to-Discrete Transition in 2D Aliphatic Layers: Abrupt Size Effect Observed via Calorimetry and Solid-State 13C NMR

Tuning Conductance in Aromatic Molecules: Constructive and Counteractive Substituent Effects

Substituent effects and local molecular shape correlations

Contact Info

Product

Resources

About

Critical Size for Bulk-to-Discrete Transition in 2D Aliphatic Layers: Abrupt Size Effect Observed via Calorimetry and Solid-State ¹³C NMR

Critical Size for Bulk-to-Discrete Transition in 2D Aliphatic Layers: Abrupt Size Effect Observed via Calorimetry and Solid-State ¹³C NMR