Effect of Allylic Groups on S_N2 Reactivity

Abstract

The activating effects of the benzyl and allyl groups on SN2 reactivity are well-known. 6-Chloromethyl-6-methylfulvene, also a primary, allylic halide, reacts 30 times faster with KI/acetone than does benzyl chloride at room temperature. The latter result, as well as new experimental observations, suggests that the fulvenyl group is a particularly activating allylic group in SN2 reactions. Computational work on identity SN2 reactions, e.g., chloride– displacing chloride– and ammonia displacing ammonia, shows that negatively charged SN2 transition states (tss) are activated by allylic groups according to the Galabov–Allen–Wu electrostatic model but with the fulvenyl group especially effective at helping to delocalize negative charge due to some cyclopentadienide character in the transition state (ts). In contrast, the triafulvenyl group is deactivating. However, the positively charged SN2 transition states of the ammonia reactions are dramatically stabilized by the triafulvenyl group, which directly conjugates with a reaction center having SN1 character in the ts. Experiments and calculations on the acidities of a variety of allylic alcohols and carboxylic acids support the special nature of the fulvenyl group in stabilizing nearby negative charge and highlight the ability of fulvene species to dramatically alter the energetics of processes even in the absence of direct conjugation.

One-Step Synthesis of Cross-Linked Ionic Polymer Thin Films in Vapor Phase and Its Application to an Oil/Water Separation Membrane

“…Also, we clearly observed the stretching and bending peaks of C−Cl at 1265 and 672 cm −1 , respectively. This result demonstrates that the highly reactive benzylic chloride in the VBC monomer 36,37 was maintained in the pVBC film, suggesting that the iCVD process does not damage the pendent functionalities in the monomer, which is fully consistent with previous observations. 20,22 Analogously, the poly(2-(dimethylamino)ethyl methacrylate) (pDMAEMA) homopolymer was also synthesized via the iCVD process, and the retention of the tertiary amine moiety in the iCVD polymer film was also confirmed by checking the FT-IR spectra of the DMAEMA monomer and the corresponding polymer film (Figure 2a).…”

“…In this regard, we chose 2-(dimethylamino)­ethyl methacrylate (DMAEMA) as a nucleophile and 4-vinylbenzyl chloride (VBC) as an electrophile (Figure c). The DMAEMA has a strong nucleophilic characteristic due to its tertiary amine moiety, whereas the VBC is a good electrophile due to the resonance-induced stability effect of benzylic carbon. − Since each monomer does not contain any ionic species, both reactants are readily vaporizable.…”

“…This tendency is consistent with previous simulation studies about Menshutkin reactivity in the gas phase. − , However, this result does not imply that this reaction is limited to VBC only. Any monomer substance having a sufficient capability of stabilization of a carbocation by a resonance effect is applicable to the Menshutkin reaction . For example, allylic carbons, tertiary (3°) carbons, and carbons of carbonyl groups can react with nucleophiles in the vapor phase.…”

Synthesis of N‐arylsulfonamides via Chan‐Lam Coupling Between Aryl Boronic Acids and N‐[(sulfonyl)imino]phenyliodinanes

“…Therefore, those reactions performed using bromo-halides (Serie 2), and chloro-halides (Serie 3) have dropped lower yields. [42] It can be explained due to the iodide is the best leaving group, followed by bromide and chloride, which means that there is a direct relation between yields and alkyl halides source. On the other hand, reactions were carried out using an unsubstituted phenylboronic acid-derived substrate (3 b) or employing electron-withdrawing substituents (3 h and 3 r).…”

Diverse Modes of Reactivity of 6‐(Chloromethyl)‐6‐methylfulvene

“…Though their dipole moments are modest in magnitude, the exocyclic double bond is highly polarizable since the corresponding resonance structure imparts 6π‐Hückel aromatic character to the cyclopentadienyl ring. We recently demonstrated through experimental and computational work that the fulvenyl group is a particularly activating allylic group in S N 2 reactions . The title compound, 6‐(chloromethyl)‐6‐methylfulvene ( 1 ), exhibits an unusually high S N 2 reactivity when compared to other allylic and benzylic halides: it reacts 30 times faster with KI/acetone than benzyl chloride at room temperature.…”