# Carbonyl Composition and Electrophilicity in Vaping Emissions of Flavored and Unflavored E-Liquids
## 3 Results and Discussions
### Global Electrophilicity and Local Site Reactivities of Carbonyls  
Global electrophilicity and local site reactivities of formaldehyde, acetaldehyde, benzaldehyde, acrolein, and _trans_-2-hexenal were calculated using computational chemistry approaches. As shown in Table 2, the global reactivity descriptors (\(I\), \(A\), \(\mu\), \(\eta\), and \(\omega\)) were calculated using the density functional theory. Values of \(I\) and \(A\) were used to calculate \(\mu\), \(\eta\), and \(\omega\) (Equations (3)-(5)), which are important for assessing global reactivity of carbonyls. Typically, the higher the \(\omega\) value, the more electrophilic the compound. When comparing the \(\omega\) values for simple carbonyls, benzaldehyde has the highest \(\omega\) value (10.43 eV), followed by formaldehyde (8.62 eV) and acetaldehyde (7.46 eV). For \(\alpha\),\(\beta\)-unsaturated carbonyls, acrolein has higher \(\omega\) (10.57 eV) than _trans_-2-hexenal (8.41 eV). As \(\omega\) works well to predict the overall reactivity of carbonyl compounds, condensed Fukui parameters are preferred to model compounds with multiple reactive sites (e.g., \(\alpha\),\(\beta\)-unsaturated carbonyls). Condensed Fukui parameters (\(f_{k}^{0}\), \(f_{k}^{-}\), \(f_{k}^{+}\), and dual-descriptor) are useful for predicting local site reactivities of \(\alpha\),\(\beta\)-unsaturated carbonyls. \(f_{k}^{0}\) is used to represent a neutral or radical attack, \(f_{k}^{-}\) represents an electrophilic attack, \(f_{k}^{+}\) represents a nucleophilic attack, and the dual-descriptor represents an electrophilic (value \(<0\)) or nucleophilic (value \(>0\)) attack [44]. Table 3 shows the calculated \(f_{k}^{+}\) values for \(\alpha\)-carbon (C\({}_{\alpha}\)), \(\beta\)-carbon (C\({}_{\beta}\)), carbonyl-carbon (C\({}_{carbonyl}\)), and carbonyl-oxygen (O\({}_{carbonyl}\)) for different carbonyls listed. The calculated \(f_{k}^{0}\), \(f_{k}^{-}\) and the dual-descriptor values are shown in Tables S3-S5. The condensed Fukui functions for C\({}_{\alpha}\) and C\({}_{\beta}\) are only applicable to \(\alpha\),\(\beta\)-unsaturated carbonyls. For simple carbonyls, C\({}_{carbonyl}\)\(f_{k}^{+}\) values are greater than O\({}_{carbonyl}\) values (Table 3). This represents that the simple carbonyls can form adducts with nucleophiles (e.g., GSH) via 1,2-carbonyl addition. For most of the \(\alpha\),\(\beta\)-unsaturated carbonyls, C\({}_{\beta}\) has highest \(f_{k}^{+}\) values, followed by C\({}_{carbonyl}\), O\({}_{carbonyl}\), and C\({}_{\alpha}\). [PERSON]'s O\({}_{carbonyl}\) has slightly higher \(f_{k}^{+}\) value than C\({}_{carbonyl}\). These results support that \(\alpha\),\(\beta\)-unsaturated carbonyls can likely form adducts with GSH (or thiol containing biomolecules) through both 1,4-conjugated and 1,2-carbonyl additions. When examining the dual-descriptor values (difference between \(f_{k}^{+}\) and \(f_{k}^{-}\)) of simple carbonyls in Table S5, all C\({}_{carbonyl}\) values are \(<\)0 (electrophilic attack) and O\({}_{carbonyl}\) values are \(>\)0 (nucleophilic attack). For all \(\alpha\),\(\beta\)-unsaturated carbonyls, their C\({}_{carbonyl}\) and C\({}_{\alpha}\) dual-descriptor values are \(>\)0. Both acrolein and _trans_-2-hexenal have O\({}_{carbonyl}\)\(<\) 0 and C\({}_{\beta}\)\(>\)