This observation indicates that 0 < EA(LiO Positive identification of LiO − was nevertheless confirmed by measuring its exact mass, and although its reactivity was difficult to probe, the ion was found to transfer an electron to O 2. 2), and this is exacerbated by the high pressure (≈10 −6 to 10 −5 torr) of argon that is introduced into the instrument to carry out the CID step. The desired ion reacts rapidly with adventitious traces of water and molecular oxygen ( Fig. mol −1 more basic than CH 3 − (see Table 1) and is predicted to be a ground-state triplet ion, this diatomic anion represents an interesting but challenging experimental target.īut this step is inefficient and difficult to carry out.This reflects the acidities of lithiated compounds, which display the opposite trend to that of first-row hydrides with Pauling electronegativity values ( Fig. mol −1], which also are predicted to be less acidic than methyllithium.For example, substitution of a lithium for a hydrogen in ammonia and water leads to weaker acids and 390.27 ± 0.02 (H 2O) vs. However, the opposite effect can also be observed. In other words, these alkali metal substituents lead to enhanced acidities in these cases. mol −1) indicate that both of these substrates are 15–16 kcal.mol −1) ( 15) and methylsodium (Δ H° acid = 401.2 kcal.Electropositive substituents such as lithium and sodium might be expected to show the opposite behavior, but BD(T)/aug-cc-pVQZ calculations on methyllithium (Δ H° acid = 401.6 kcal the electronegativity of X for first-row hydrides ( Fig. However, the conjugate bases of lithiated compounds are difficult to prepare in the gas phase, and almost nothing is known about them because the neutral acids tend to be involatile, moisture sensitive, and pyrophoric.Įlectronegative substituents are well known to stabilize negative ions and increase acidities, and this is reflected in a plot of Δ H° acid(HX) vs. To decrease the acidity of a compound and make a stronger base, one might employ an electropositive substituent such as lithium.
Electronegative substituents stabilize negative ions and increase acidities, as reflected by the first-row hydrides. mol −1 ( 4), and CH 3CH 2 − and (CH 3) 2CH − are predicted to be unbound with respect to electron detachment ( 7).This is not surprising because the electron affinity of methyl radical is only 1.8 ± 0.7 kcal mol −1 less acidic than methane ( 7), but their conjugate bases have never been observed ( 8, 9).Kinetic measurements indicate that ethane and the secondary position of propane are 2–3 kcal Alkyl groups are polarizable but also are generally electron-releasing and, depending on which influence is larger, can destabilize anions.
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