Relationship between substituent effect and aromaticity – Part III: naphthalene as a transmitting moiety for substituent effect

Molecular geometry of 10 isomeric nitronaphtholate ions (excluding peri‐ and ortho‐type substituted systems), 1‐ and 2‐naphtholate ions, 1‐ and 2‐nitronaphthalene, meta‐ and para‐nitrophenolate, phenolate, and nitrobenzene were optimized at B3LYP/6‐311G** level of approximation. Substituent effect stabilization energy (SESE), geometry‐based aromaticity index HOMA, magnetism‐based indices NICS, NICS(1), NICS(1)_zz, and parameters characterizing Bond Critical Points (BCP) (ρ, ?²ρ, ellipticity, ion/cov) of the Bader AIM theory were used to characterize transmitting properties for substituent effect through the naphthalene moiety. It results from our study that the studied systems could be clearly divided into two groups, (i) a para‐type group, where the intramolecular charge transfer between the π‐electron donating and π‐electron accepting substituents can be described by canonical forms with charge separation (as in the case of para‐nitrophenolate) and (ii) a meta‐type group, where this transfer requires using canonical forms with double charge separation (as in the case of meta‐nitrophenolate). Copyright © 2007 John Wiley & Sons, Ltd.     

Excited‐state substituent constants σ from substituted benzenes

In this work, 13 compounds of 4,4′‐disubstituted stilbenes and 5 compounds of 3‐methyl‐4′‐substituted stilbenes were prepared and their UV spectra were measured. A new substituent effect constant, namely excited‐state substituent constant, was proposed, which was calculated directly from the UV absorption energy data of substituted benzenes. The investigation result shows that the proposed constant is different from the existing polar substituent constants and radical substituent constants in nature. The availability of the new constant was confirmed by the good correlations with the UV absorption energy of four kinds of compounds, 1,4‐disubstituted benzenes, 4,4′‐disubstituted stilbenes, substituted ethenes, and m‐Y‐substituted aromatic compounds. It is expected that the excited‐state substituent constant can be applied in QSPR study on organic compounds at the excited state. Copyright © 2008 John Wiley & Sons, Ltd.     

The β‐silicon effect. 4: substituent effects on the solvolysis of 1‐alkyl‐2‐(aryldimethylsilyl)ethyl trifluoroacetates

Solvolysis rates of 2‐(aryldimethylsilyl)‐1‐methylethyl and 2‐(aryldimethylsilyl)‐1‐tert‐butylethyl trifluoroacetates were determined conductimetrically in 60% (v/v) aqueous ethanol. The effects of aryl substituents at the silicon atom on the solvolysis rates at 50 °C were correlated with parameters of r⁺ = 0.15 with the Yukawa–Tsuno equation, giving ρ values of ?1.5 for both secondary α‐Me and α‐tert‐Bu systems. The ρ values for those secondary systems are less negative than ?1.75 for the 2‐(aryldimethylsilyl)ethyl system that proceeds by the Eaborn (non‐vertical) mechanism, while they are distinctly more negative than ?0.99 for 2‐(aryldimethylsilyl)‐1‐phenylethyl system that should proceed by the Lambert (vertical) mechanism. There was a fairly linear relationship between the reaction constants (ρ) for the β‐silyl substituent effects and the solvolysis reactivities for a series of β‐silyl substrates. The solvolyses of the α‐Me and tert‐Bu substrates proceed through the transition state (TS) with an appreciable degree of the β‐silyl participation, close to the Eaborn (non‐vertical) TS rather than to the Lambert (vertical) TS. Copyright © 2010 John Wiley & Sons, Ltd.     

Substituent effects on the 13C NMR chemical shifts of the imine carbon in N‐(4‐X–benzylidene)‐4‐(4‐Y–styryl) anilines

Long‐range electronic substituent effects were targeted using the substituent dependence of δ_C(C═N), and specific cross‐interactions were explored extendedly. A wide set of N‐(4‐X–benzylidene)‐4‐(4‐Y–styryl) anilines, p‐X–C₆H₄CH═NC₆H₄CH═CHC₆H₄–p‐Y (X = NMe₂, OMe, Me, H, Cl, F, CN, or NO₂; Y = NMe₂, OMe, Me, H, Cl, or CN) were prepared for this study, and their ¹³C NMR chemical shifts δ_C(C═N) of C═N bonds were measured. The results show that both the inductive and resonance effects of the substituents Y on the δ_C(C═N) of p‐X–C₆H₄CH═NC₆H₄CH═CHC₆H₄–p‐Y are less than those of the substituents Y in p‐X–C₆H₄CH═NC₆H₄–p‐Y. Moreover, the sensitivity of the electronic character of the C═N function to electron donation/electron withdrawal by the substituent X or Y attenuates as the length of the conjugated chain is elongated. It was confirmed that the substituent cross‐interaction is an important factor influencing δ_C(C═N), not only when both X and Y are varied but also when either X or Y is fixed. The long‐range transmission of the specific cross‐interaction effects on δ_C(C═N) decreases with increasing conjugated distance between X and Y. The results of this study suggest that there is a long‐range transmission of the substituent effects in p‐X–C₆H₄CH═NC₆H₄CH═CHC₆H₄–p‐Y. Copyright © 2012 John Wiley & Sons, Ltd.     

Substituent effect on local aromaticity in mono and di‐substituted heterocyclic analogs of naphthalene

A quantitative study on local aromaticity has been performed on a series of mono‐ and di‐substituted biheterocycles (quinoline, isoquinoline, quinoxaline, quinazoline). Three electronically based indices (PDI, ATI, and FLU) have been employed to investigate the substituent effect on the π‐electron delocalization in both heterocycle and benzenoid rings. Three typical substituents (Cl, OCH₃, and CN) with different inductive and resonance power have been selected. Generally, substituent causes a reduction in aromaticity irrespective of whether it is electron attracting or electron donating. It is shown that the maximum aromaticity exhibits a similar trend of Cl > CN > OCH₃ for all the studied rings. Moreover, it is found that the substituent situation with respect to the heteroatom has a significant influence on the aromaticity. It results from our study that in di‐substituted derivatives, irrespective of whether the two substituents form a meta or para isomer, they preferably choose the position which leads to the maximum aromaticity character. Copyright © 2009 John Wiley & Sons, Ltd.     

Diastereofacial selectivity in some 4‐substituted (X) 2‐adamantyl derivatives: electronic versus steric effects

π‐Facial selectivity data for the reduction and methylation of some 4^ax‐substituted (X) 2‐adamantanones ( 3 , Y = O) as well as the nucleophilic trapping of secondary and tertiary 4^ax‐substituted (X)‐2‐adamantyl cations ( 4 ; R = H and CH₃, respectively) and the 4‐methylene‐2‐adamantyl radical ( 8 ) are presented. The pronounced anti‐face selectivities observed for ( 3 , Y = O and 4 , R = CH₃) emphasize the importance of the steric factor as expected for systems with a strong steric bias. However, the dominant syn‐face capture of 4 (R = H) was completely unexpected and highlights a subtle interplay between steric and electronic effects. Finally, the very high anti‐face stereoselectivity for the trapping of ( 8 ) with the trimethylstannyl anion (Me₃Sn^?) is rationalized in terms of an electrostatic effect overwhelming the steric factor. Copyright © 2007 John Wiley & Sons, Ltd.     

An experimental investigation of substituent effects on the formation of 2,3‐dihydroquinazolin‐4(1H)‐ones: a kinetic study

The effect of different substituents on the kinetics of the reactions between 2‐amino‐benzamide and some of benzaldehyde derivatives have been spectrally investigated in the presence of formic acid. The proposed mechanism were challenged due to the determination of rate‐determining step (RDS) and also, to obtain the general rate law of the reaction. For all substituents, the reactions followed the second‐order kinetics and the partial orders of reactions were recognized with respect to each reactant. Electron withdrawing substituents on benzaldehyde ring increased the rate of reaction. Kinetic values (k and E_a) and associated activation parameters (ΔH^?, ΔG^? and ΔS^?) of the reactions were determined. Both the Arrhenius and the Eyring equations were used to calculate activation energy. Comparison of magnitude of and T showed that the reactions were enthalpy controlled. Isokinetic plots for the reactions were plotted and linear relationship between and recognized that relative contribution of enthalpy and entropy to the overall free energy was the same in the reactions.     

Comparison of the 13C (C = N) chemical shifts of substituted N‐(phenyl‐ethylene)‐anilines and substituted N‐(benzylidene)‐anilines

Comparison of ¹³C NMR of C = N bond chemical shifts δ_C(C = N) in substituted N‐(phenyl‐ethylene)‐anilines XArC(Me) = NArY (XPEAYs) with that in substituted N‐(benzylidene)‐anilines XArCH = NArY (XBAYs) was carried out. The δ_C(C = N) of 61 samples of XPEAYs were measured, and the substituent effect on their δ_C(C = N) were investigated. The results show the factors affecting the δ_C(C = N) of XPEAYs are quite different from that of XBAYs. A penta‐parameter correlation equation was obtained for the 61 compounds, which has correlation coefficient 0.9922 and standard error 0.12 ppm. The result indicates that, in XPEAYs, the inductive effects of substituents X and Y are major factors affecting the δ_C(C = N), while the conjugative effect of them have very little effect on the δ_C(C = N) and can be ignored. The substituent‐specific cross‐interaction effects between X and Y and between Me of C = N bond and substituent Y are important factors affecting the δ_C(C = N). Also, the excited‐state substituent parameter of substitute Y has certain contribution to the δ_C(C = N). Copyright © 2015 John Wiley & Sons, Ltd.     

Breathing viability into cyclonona‐3,5,7‐trienylidenes via α‐dimethyl and ά‐moieties at DFT

Cyclonona‐3,5,7‐trienylidene ( 1 ) changes from being a transition state (TS) to minimum states when substituted by α‐methyl groups and ?‐X, where X = CMe₂, NMe, PMe, O, S, cyclopropyl, and SiMe₂ ( 2 , 3 , 4 , 5 , 6 , 7 , 8 , respectively) at density functional theory. Specifically, the parent carbene 1 exhibits a negative vibrational force constant and proves to be an unreachable electrophilic TS while shows C_s symmetry with an NBO atomic charge of +0.70 on its carbenic center. It has a triplet ground state with a rather small singlet‐triplet energy gap (ΔE_s–t = ?4.1 kcal/mol). In contrast, all of its seven scrutinized derivatives enjoy reachable global minima, with C₁ symmetry, desired nucleophilicity, and singlet closed shell (S_cs) ground states (for all but 8 which remains triplet). Stability is indicated by relative ΔE_s–t values: 2 > 3 > 4 > 5 > 6 > 7 > 1 > 8 . The highest ΔE_s–t as well as NBO carbenic atomic negative charge (?0.74) are displayed by 2 . Our carbenes ( 2 , 3 , 4 , 5 , 6 , 7 ) appear more nucleophilic than the synthesized N‐heterocyclic carbenes (imidazol‐2‐ylidenes). Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of substituent on the UV–Vis spectra: an extension from disubstituted to multi‐substituted benzylideneanilines

For studying the substituent effects on the ν_max of substituted benzylideneanilines (XBAYs) systematically, 12 samples of 3,3′‐disubstituted XBAYs and 52 samples of multi‐substituted XBAYs were synthesized, and the substituent effects on their ν_max were investigated in this paper. A modified regression equation quantifying the ν_max of 4,4′/4,3′/3,4′/3,3′‐disubstituted and multi‐substituted XBAYs (shown as Eq. 3 ) was obtained. The results showed that the substituent effects on the ν_max of 3,3′‐substituted and multi‐substituted XBAYs became more complicated. In Eq. 3 , the contributions of the meta‐parameters to the ν_max of XBAYs were different from those of the corresponding para‐parameters. For the substituent cross‐interaction effects, there is no difference whatever the substituents are at meta‐position or para‐position. Compared with Eq. 1 , Eq. 3 obtained in this paper has a wider application and more accuracy in quantifying the ν_max of substituted XBAYs. Copyright © 2016 John Wiley & Sons, Ltd.     

Transmission of polar substituent effects across the cubane ring system: 19F substituent chemical shifts (SCS) of 4‐substituted (X) cub‐1‐yl fluorides revisited

¹⁹F NMR shieldings of 4‐substituted (X) cub‐1‐yl fluorides ( 4 ) for a set of substituents (X?H, NO₂, CN, NC, CF₃, COOH, F, Cl, HO, NH₂, CH₃, Si(CH₃)₃, Li, O^? and NH) covering a wide range of electronic substituent effects were calculated using the DFT‐GIAO theoretical model. The level of theory, B3LYP/6‐311+G(2d,p), provided ¹⁹F substituent chemical shifts (SCS) in good agreement with experimental values where known. By means of NBO analysis, various molecular parameters were obtained from the optimized geometries. Linear regression analysis was employed to explore the relationship between the calculated ¹⁹F SCS and polar field, resonance and group electronegativity substituent constants (σ_F, σ_R and σ_x, respectively) and also the NBO derived molecular parameters (fluorine natural charges (Q_n), electron occupancies on fluorine of lone pairs (n_F) and occupation number of the C? F antibonding orbital (σ_CF*)). The key determining parameters appear to be n_F and σ_CF*(occup). Both factors are a function of the electrostatic field influence of the substituent (σ_F effect) but are counteractive in their influence on the shifts. No evidence for a significant resonance effect influence on the shifts could be identified. Copyright © 2009 John Wiley & Sons, Ltd.     

Substituent effect investigation of 3‐(2, 4‐dichlorophenyl)‐1‐(4′‐X‐phenyl)‐2‐propen‐1‐one. Part 1. Correlation analysis of 13C NMR chemical shifts

A series of substituted chlorinated chalcones namely, 3‐(2,4‐dichlorophenyl)‐1‐(4′‐X‐phenyl)‐2‐propen‐1‐one, have been synthesized, X being H, NH₂, OMe, Me, F, Cl, CO₂Et, CN, and NO₂. Dual substituent parameter (DSP) models of ¹³C NMR chemical shift (CS) have revealed that π‐polarization concept could be utilized to explain the reverse field effect at CO, the enhanced substituent field effect at CO, C‐2, and C‐5, and the decreased sensitivity of substituent field effect at C‐6. Chlorine atoms dipole direction at the benzylidene ring either enhances or reduces substituent effect depending on how they couple with the substituent dipole at the probe site. The correlation of ¹³C NMR CS of C‐2, C‐5, and C‐6 with σ and σ indicates that chlorine atoms in the benzylidine ring deplete the ring from charges. Both MSP of Hammett and DSP of Taft ¹³C NMR CS models give similar trends of substituent effects at C‐2, C‐5, and C‐6. However, the former fail to give a significant correlation for CO and C‐6 ¹³C NMR CS. MSP of σ_q and DSP of Taft and Reynolds models significantly correlated ¹³C NMR CS of C_β. MSP of σ_q fails to correlate C‐1′ ¹³C NMR CS. Investigation of ¹³C NMR CS of non‐chlorinated chalcones series: 3‐phenyl‐1‐(4′‐X‐phenyl)‐2‐propen‐1‐one has revealed similar trends of substituent effects as in the chlorinated chalcones series for C‐1′, CO, C_α, and C_β. In contrast, the substituent effect of the non‐chlorinated chalcone series at C‐2, C‐5, and C‐6 did not correlate with any substituent constant. Copyright © 2010 John Wiley & Sons, Ltd.     

Conformational analysis of 3,3‐dimethyl‐3‐silathiane, 2,3,3‐trimethyl‐3‐silathiane and 2‐trimethylsilyl‐3,3‐dimethyl‐3‐silathiane—preferred conformers,barriers to ring inversion and substituent effects

The first conformational analysis of 3‐silathiane and its C‐substituted derivatives, namely, 3,3‐dimethyl‐3‐silathiane 1 , 2,3,3‐trimethyl‐3‐silathiane 2 , and 2‐trimethylsilyl‐3,3‐dimethyl‐3‐silathiane 3 was performed by using dynamic NMR spectroscopy and B3LYP/6‐311G(d,p) quantum chemical calculations. From coalescence temperatures, ring inversion barriers ΔG^≠ for 1 and 2 were estimated to be 6.3 and 6.8 kcal/mol, respectively. These values are considerably lower than that of thiacyclohexane (9.4 kcal/mol) but slightly higher than the one of 1,1‐dimethylsilacyclohexane (5.5 kcal/mol). The conformational free energy for the methyl group in 2 (?ΔG° = 0.35 kcal/mol) derived from low‐temperature ¹³C NMR data is fairly consistent with the calculated value. For compound 2 , theoretical calculations give ΔE value close to zero for the equilibrium between the 2 ‐Me_ax and 2 ‐Me_eq conformers. The calculated equatorial preference of the trimethylsilyl group in 3 is much more pronounced (?ΔG° = 1.8 kcal/mol) and the predominance of the 3 ‐SiMe_{3 eq} conformer at room temperature was confirmed by the simulated ¹H NMR and 2D NOESY spectra. The effect of the 2‐substituent on the structural parameters of 2 and 3 is discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

Tuning the absorption spectra and nonlinear optical properties of D‐π‐A azobenzene derivatives by changing the dipole moment and conjugation length: a theoretical study

The optical properties of several azobenzene derivatives were modulated by varying the dipole moments and conjugation lengths of the D‐π‐A systems. The relationship between the structure and absorption spectrum and polarizability was studied in the gas phase, THF and MeOH solutions, respectively, by using the density functional theory. The calculated absorption spectra and second‐order polarizabilities are in good agreement with the available experimental observations. In comparison with the D‐π‐A monomer, the H‐shaped D‐π‐A dimer almost doubles the dipole moments and hence increases the second‐order polarizabilities, without a significant shift in the maximum absorption bands. The addition of another azobenzol group between electron‐donating and ‐accepting groups increases the second‐order polarizabilities by 4–6 times, but leads to an evident red‐shift of about 65–80 nm in spectra. The relative second‐order polarizability of the halogen‐substituted derivatives is in the sequence of ? CF₃ > ? F > ? Cl > ? Br, without obvious substituent effects on the optical transparency. The D‐π‐A chromophores with the strong electron‐donating (amino) and ‐accepting (acetyl) substituent present the larger second‐order polarizabilities, at the cost of about 20 nm red‐shift of the maximum absorption lengths relative to the halogen‐substituted species. It is also demonstrated that both the linear and nonlinear optical properties augment with the increase in solvent polarity, accompanied by a red‐shift in the wavelengths of maximum absorption by about 18 and 23 nm, respectively, in THF and MeOH solutions. The changes in optical properties upon the structural modifications are further rationalized by the electronic structures of various H‐shaped dimers. Copyright © 2010 John Wiley & Sons, Ltd.     

Calculated polar substituent effects on the stability of 4‐substituted(X) ‐ cub‐1‐yl and ‐bicyclo[2.2.2]oct‐1‐yl cations: a DFT study

The effects of substituents on the stability of 4‐substituted(X) cub‐1‐yl cations ( 2 ), as well as the benchmark 4‐substituted(X) bicyclo[2.2.2]oct‐1‐yl cation systems ( 7 ), for a set of substituents (X = H, NO₂, CN, NC, CF₃, COOH , F, Cl, HO, NH₂, CH₃, SiH₃, Si(CH₃)₃, Li, O^?, and NH) covering a wide range of electronic substituent effects were calculated using the DFT theoretical model at the B3LYP/6‐311 + G(2d,p) level of theory. Linear regression analysis was employed to explore the relationship between the calculated relative hydride affinities (ΔE, kcal/mol) of the appropriate isodesmic reactions for 2 / 7 and polar field/group electronegativity substituent constants (σ_F and σ_χ, respectively). The analysis reveals that the ΔE values of both systems are best described by a combination of both substituent constants. This highlights the distinction between through‐space and through‐bond electronic influences characterized by σ_F and σ_χ, respectively. Copyright © 2010 John Wiley & Sons, Ltd.     

Calculated polar substituent effects on the stability of 3‐substituted(X) bicyclo[1.1.1]pent‐1‐yl cations and 4‐substituted(X) bicyclo[2.2.1]hept‐1‐yl cations: a DFT study

The effects of substituents on the stability of 3‐substituted(X) bicyclo[1.1.1]pent‐1‐yl cations (3) and 4‐substituted(X) bicyclo[2.2.1]hept‐1‐yl cations (4), for a set of substituents (X = H, NO₂, CN, NC, CF₃, CHO, COOH , F, Cl, HO, NH₂, CH₃, SiH₃, Si(CH₃)₃, Li, O^?, and NH₃⁺) covering a wide range of electronic substituent effects were calculated using the DFT theoretical model at the B3LYP/6‐311 + G(2d,p) and B3LYP/6‐31 + G (d) levels of theory, respectively. Linear regression analysis was employed to explore the relationship between the calculated relative hydride affinities (ΔE, kcal/mol) of the appropriate isodesmic reactions for 3/4 and polar field/group electronegativity substituent constants (σ_F and σ_χ, respectively). The analysis reveals that the ΔE values for both systems are best described by a combination of both substituent constants. The result highlights the importance of the σ_χ dependency of charge delocalization in these systems. Copyright © 2012 John Wiley & Sons, Ltd.     

Substituent effects on acidity of aryl‐substituted fluoroalkanes: a computational study

The gas‐phase acidities (GA) of various aryl‐substituted fluoroalkanes, XC₆H₄CH(R¹)R², were calculated at the B3LYP/6‐311 + G(d,p)//B3LYP/6‐311 + G(d,p). The acidity values of alkanes having a common substituent X varied significantly with the change of R¹ and R². Their changes in acidity of 1 and 2 having two strong electron‐withdrawing groups (CF₃ or C₂F₅) at the deprotonation site and 8 , 9 , 10 , 11 having no fluorine atom at β‐position were linearly correlated with the corrected number of fluorine atoms contained in the fluorinated alkyl group (R² > 0.999). On the other hand, the GA values of β‐fluorine substituted alkanes ( 3 , 4 , 5 , 6 , 7 ) deviated in a stronger acid direction from the line. The enhanced acidity was attributed to the additional stabilization of the conjugate anion caused by the β‐fluorine negative hyperconjugation. The magnitude of β‐fluorine negative hyperconjugation of the fluorinated alkyl group (ΔG^o_β‐F) given by the deviations from the line decreased with increasing electron‐withdrawing ability of substituent X on the benzene ring, indicating that β‐fluorine negative hyperconjugation competes with the electronic effect of the substituent X. The GA_el values obtained by subtraction ΔG^o_β‐F from the apparent GA value were successfully correlated in terms of the Yukawa–Tsuno equation. The obtained ρ_el and r^?_el values were linearly related to the GA_el value of the respective phenyl‐substituted fluoroalkanes, supporting our previous conclusion that the ρ and r^? values for the substituent effect caused by the electronic effects of the substituent on the acidity are determined by the thermodynamic stability of the parent ion (ring substituent = H). Copyright © 2015 John Wiley & Sons, Ltd.     

Enols of 2‐nitro‐ and related 2‐substituted malonamides

The structures of 2‐substituted malonamides, YCH(CONR¹R²)CONR³R⁴ (Y = Br, SO₂Me, CONH₂, COMe, and NO₂) were investigated. When Y = Br, R¹R² = R³R⁴ = HEt; Y = SO₂Me, R¹–R⁴ = H and for Y = CONH₂ or CONHPh, R¹–R⁴ = Me, the structure in solution is that of the amide tautomer. X‐ray crystallography shows solid‐state amide structures for Y = SO₂Me or CONH₂, R¹–R⁴ = H. Nitromalonamide displays an enol structure in the solid state with a strong hydrogen bond (O^…O distance = 2.3730 Å at 100 K) and d(OH) ≠ d(O^…H). An apparently symmetric enol was observed in solution, even in appreciable percentages in highly polar solvents such as DMSO‐d₆, but K_enol values decrease on increasing the solvent polarity. The N,N′‐dimethyl derivative is less enolic. Acetylmalonamides display a mixture of enol on the acetyl group and amide in non‐polar solvents, and only the amide in DMSO‐d₆. DFT calculations gave the following order of pK_enol values for Y: H > CONH₂ > COMe ≥ COMe (on acetyl) ≥ MeSO₂ > CN > NO₂ in the gas phase, CHCl₃, and DMSO. The enol on the C?O group is preferred to the aci‐nitro compound, and the N? O? H^…O?C is less favored than the C?O? H^…O?C hydrogen bond. Copyright © 2009 John Wiley & Sons, Ltd.     

The nature of the electronic factor governing diastereofacial selectivity in remotely substituted (X) 2‐adamantyl cations: 5‐X versus 4‐X substitution

A limited series of 4^eq‐substituted (X) 2‐methyleneadamantanes ( 6 , Y?CH₂, X?F, Cl, Br, I, and SnMe₃) has been synthesized and diastereoselectivities for their hydrochlorination (HCl/CH₂Cl₂) have been determined. Diastereoselectivities for the fluorination (DAST/CH₂Cl₂) of secondary alcohol mixtures, obtained from the hydride reduction of the precursor ketones ( 6 ,Y?O) to the alkenes, have also been measured. A comparison of this selectivity data for nucleophilic trapping of 4^eq‐substituted (X) 2‐adamantyl cations ( 4 , R?H and Me) with the corresponding information for 5‐substituted (X) 2‐adamantyl cations ( 1 , R?H and Me) has revealed important distinctions between the two series. In particular, whereas extended hyperconjugative effects appear to be the predominant electronic effect governing facial selectivity in the 5,2‐series, electrostatic influences prevail in the 4,2‐disposition. Copyright © 2007 John Wiley & Sons, Ltd.