Acetaldehyde Lewis structure

There are many other molecules in which some of the electrons are less localized than is implied by a single Lewis structure and can therefore be represented by two or more resonance structures. For example, the three bonds in the carbonate ion all have the same length of 131 pm, which is intermediate between that of the C—O single bond in methanol (143 pm) and that of the C=0 double bond in methanal (acetaldehyde) (121 pm). So the carbonate ion can be conveniently represented by the following three resonance structures ... 

In this case, no proton has been transferred, so this is not a Brpnsted-Lowry acid-base reaction. Instead, a bond has formed between the C = 0 carbon atom and the oxygen of the CH3—O group. Drawing the Lewis structures helps to show that the CH3—O group (the nucleophile in this reaction) donates the electrons to form the new bond to acetaldehyde (the electrophile). This result agrees with our intuition that a negatively charged ion is likely to be electron-rich and therefore an electron donor. 

Example 1.2. 77ie Lewis structure for acetaldehyde, CHjCHO. 

Problem 1.11 Draw both a Lewis structure and a line-bond structure for acetaldehyde, CH3CHO. 

Acetaldehyde can be converted into the sedative chloral hydrate (the Mickey Finn or knockout drops often mentioned in detective stories). In the first step of the reaction that forms chloral hydrate, acetaldehyde, CH3CHO, changes to its isomer, CH2CHOH. Draw a reasonable Lewis structures for each of these isomers. 

Step 6 All of the atoms in both structures have their most common bonding pattern, so we have two reasonable Lewis structures representing isomers. Structure 1 is acetaldehyde (or ethanal) and structure 2 is ethenol. 

PROBLEM 2.42 Write Lewis structures for ethane, ethylene, acetylene, ethanol, ethanethiol, tetraethylammonium ion, diethylphosphine, the imine of diethyl ketone, diethylborane, tetraethylborate ion, diethyl ether, diethyl sulfide, acetaldehyde, acetone, acetic acid, ethyl acetate, acetamide, acetyl chloride, propanenitrile, ethyl fluoride, and ethyl chloride. Show nonbonding electrons as dots and electrons in bonds as lines. 

Write the Lewis structure for the molecuie. SOLUTION Brp3 has 28 valence electrons and the following Lewis structure F . T Br— F . . . F SOLUTION Acetaldehyde has 18 valence electrons and the following Lewis structure H 0 1 II H—C—C—H 1 H... 

PRACTICE EXAMPLE B Write plausible Lewis structures for (a) formic acid, HCOOH, and (b) acetaldehyde, CH3CHO. 

The addition reaction of allylsilane to acetaldehyde with BF3 as the Lewis acid has been modeled computationally.95 The lowest-energy TSs found, which are shown in Figure 9.2, were of the synclinal type, with dihedral angles near 60°. Although the structures are acyclic, there is an apparent electrostatic attraction between the fluorine and the silicon that imparts some cyclic character to the TS. Both anti and syn structures were of comparable energy for the model. However, steric effects that arise by replacement of hydrogen on silicon with methyl are likely to favor the anti TS. 

Finally, carbonyls can bind two metals at once. The crystal structure of a bridging (p,), q -bound acetaldehyde complex, for example, shows the carbonyl coordinated to two molybdenum atoms (Figure 38). It appears that in this structure the carbonyl utilizes its it as well as its lone pair electrons to bond to the two metal centers. Conceptually one can think of this molybdenum complex as a bidentate Lewis acid that chelates the carbonyl group. 

Denmark has spectroscopically examined the reaction of both allyl- and 2-bute-nylstannanes with aldehydes using the Lewis acids SnCU and BF3-OEt2 [73, 82]. First, the metathesis of both allyltributylstannane and tetraallyltin with SnCl4 was determined (by C NMR spectroscopy) to be instantaneous at -80 °C. The reaction of allyltributylstannane with a complexed aldehyde was detemiined to be significantly more complicated. When a molar equivalent of SnCU per aldehyde was employed, metathesis was determined to be the preferred pathway for aldehydes. When one half a molar equivalent of SnC per aldehyde is used, the reaction pathways and product distribution become very sensitive to both the aldehyde structure and addition order. A spectrum of mechanistic pathways was documented ranging from direct addition (acetaldehyde) to complete metathesis (pivalalde-hyde) to a competitive addition and metathesis (4-t-butylbenzaldehyde). The results obtained with a molar equivalent of SnCl4 are most relevant, as this reagent stoichiometry is most commonly used in the addition reactions. 

Draw a Lewis formula and a three-dimensional structure for each of the following polycentered molecules. Indicate hybridizations and bond angles at each carbon atom, (a) butane, C4H3Q (b) propene, H2C=CHCH3 (c) 1-butyne, HC=CCH2CH3 (d) acetaldehyde, CH3CHO. 

Many carbonyl addition and substitution reactions are carried out under acidic conditions or in the presence of Lewis acids. Qualitatively, protonation or complexation increases the electrophilicity of the carbonyl group. The structural effects of protonation have been examined for formaldehyde, acetaldehyde, acetone, formamide, and formyl fluoride. These effects should correspond to those in more complex carbonyl compounds. Protonation results in a substantial lengthening of the C=0 bond. The calculated [B3LYP/ 6-31-H-G(phase proton affinities reflect the trend of increasing basicity with donor groups (CH3, NH2) and decreased basicity for fluorine. 

The effect of Lewis acids has also been examined computationally. In agreement with crystal structure determinations, Lewis acids such as BF3 normally adopt an anti structure for aldehydes. Despite the unfavorable steric effect in acetone, the calculated (MP2/6-31G) energy of complexation with BF3 is nearly as high as for acetaldehyde, presumably owing to the additional electron donation by the methyl groups. ... 

Various other 2,4,6-trisubstituted-l,3,5-trioxanes obtained by cyclotrimerization of the corresponding aldehydes have been reported (cf. Scheme 70 Table 17) common catalysts employed were, besides protic acids, zeolites, bentonitic earth, Lewis acids, heteropoly acids, organic metal oxides, and ion-exchange resins. When X-ray structures were reported, the chair conformer with the substituents in equatorial positions was always found (e.g., <19988417>). Also, the trimerization of acetaldehyde and propionaldehyde in the presence of SO2 has been reported <1983ZOB1787> wherein the aldehydes and SO2 initially form CT complexes. In the case of acetaldehyde, the corresponding enthalpy and entropy of complexation were determined to be —ISkJmoL and —32JmoL respectively. 

CHjCHO Acetaldehyde is the prototype species for a wide variety of aliphatic carbonyl compounds. The photochemistry and electronic spectroscopy have been reviewed by Lee and Lewis The electronic structures in the carbonyl group of acetaldehyde are similar to those of formaldehyde in that the low lying valence and Rydberg levels have about the same energy. For example, n k excitation in both species gives rise to a weak absorption at 350-250 nm. The first Rydberg n - 3s excitation is found as a line-like feature at 182 nm, compared to the 174 nm band of CHjO. 

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