20.8) Draw the products when the following compounds are treated with NaBH4 in MeOH. a) b) c)
20.9) What reagent is needed to carry out the reaction below? Two reagents are needed to carry out this reaction. First, the (S)-CBS reagent to produce the R-enantiomer. Followed by H2O to protonate the alcohol.
20.12) Draw the products of LiAlH4 reduction of each compound. a) b) c)
20.14) Predict the products of these compounds when treated with the following reagents. a) b) No reaction
20.15) Predict the products in the following reactions. a) No Reaction b)
20.16) Predict the products of the compound below when reacted with each reagent. a) b)
c) d) e)
20.22) Draw the products (including stereochemistry) of the following reactions. a) b)
20.26) Draw out the products when each compound is treated with 2 equivalents of CH3CH2CH2CH2MgBr followed by H2O? a) b) c)
20.28) Tertiary alcohols can also be formed by reacting dimethyl carbonate with excess Grignard reagent. Draw out a mechanism for the following reaction.
20.32) What carboxylic acid is formed from each aqlkyl halide when treated with Mg, CO2 and H2O? a)
20.34) Draw the products of each compound when treated with either dimethylcuprate or lithium acetylide followed by water. a)
20.36) Synthesize each of the following using cyclohexanol, ethanol and any other inorganic reagent. a)
Aldehydes and Ketones—Nucleophilic Addition Introduction Aldehydes and ketones contain a carbonyl group. An aldehyde contains at least one H atom bonded to the carbonyl carbon, whereas the ketone has two alkyl or aryl groups bonded to it. Two structural features determine the chemistry and properties of aldehydes and ketones.
Aldehydes and Ketones—Nucleophilic Addition Introduction • Aldehydes and ketones react with nucleophiles. • As the number of R groups around the carbonyl carbon increases, the reactivity of the carbonyl compound decreases, resulting in the following order of reactivity:
Nomenclature of Aldehydes • If the CHO is bonded to a chain of carbons, find the longest chain containing the CHO group, and change the –e ending of the parent alkane to the suffix –al. If the CHO group is bonded to a ring, name the ring and add the suffix –carbaldehyde. • Number the chain or ring to put the CHO group at C1, but omit this number from the name. Apply all the other usual rules of nomenclature.
Like carboxylic acids, many simple aldehydes have common names that are widely used. • A common name for an aldehyde is formed by taking the common parent name and adding the suffix -aldehyde. • Greek letters are used to designate the location of substituents in common names.
Nomenclature of Ketones • In the IUPAC system, all ketones are identified by the suffix “one”. • Find the longest continuous chain containing the carbonyl group, and change the –e ending of the parent alkane to the suffix -one. • Number the carbon chain to give the carbonyl carbon the lowest number. Apply all of the usual rules of nomenclature. • With cyclic ketones, numbering always begins at the carbonyl carbon, but the “1” is usually omitted from the name. The ring is then numbered clockwise or counterclockwise to give the first substituent the lower number.
Most common names for ketones are formed by naming both alkyl groups on the carbonyl carbon, arranging them alphabetically, and adding the word “ketone”. • Three widely used common names for some simple ketones do not follow this convention:
Sometimes, acyl groups must be named as substituents. The three most common acyl groups are shown below:
Spectroscopic Properties—IR Spectra • Aldehydes and ketones exhibit a strong peak at ~1700 cm-1 due to the C=O. • The sp2 hybridized C—H bond of an aldehyde shows one or two peaks at ~2700 –2830 cm-1. Figure 21.3 The IR spectrum of propanal, CH3CH2CHO
Most aldehydes have a carbonyl peak around 1730 cm-1, whereas for ketones, it is typically around 1715 cm-1. • Ring size affects the carbonyl absorption in a predictable manner.
Conjugation also affects the carbonyl absorption in a predictable manner. Figure 21.4 The effect of conjugation on the carbonyl absorption in an IR spectrum
Spectroscopic Properties—NMR Spectra Aldehydes and ketones exhibit the following 1H and 13C NMR absorptions. • The sp2 hybridized C—H proton of an aldehyde is highly deshielded and absorbs far downfield at 9-10 ppm. Splitting occurs with protons on the carbon, but the coupling constant is often very small (J = 1-3 Hz). • Protons on the carbon to the carbonyl group absorb at 2-2.5 ppm. Methyl ketones, for example, give a characteristic singlet at ~2.1 ppm. • In a 13C NMR spectrum, the carbonyl carbon is highly deshielded, appearing in the 190-215 ppm region.
Figure 21.5 The 1H and 13C NMR spectra of propanal, CH3CH2CHO
Preparation of Aldehydes and Ketones Common methods to synthesize aldehydes:
Aldehydes and ketones are also both obtained as products of the oxidative cleavage of alkenes.
Which compound is most reactive toward nucleophilic addition? B is most reactive. The less R groups attached to the carbonyl the less sterically hindered it is and thus more reactive.
Which is more reactive and why? B is more reactive because it isn’t resonance stabilized like A.
Which of these compounds is 2-isobutyl-3-isopropylhexanal? C is the correct answer.
Which compound is 5-ethyl-4-methyl-3-octanone B is the correct answer.
Which of the following is the name of the compound below? • 4-methyl-3-hexanone • Isopropyl ethyl ketone • 3-methyl-4-hexanone] • sec-butyl ethyl ketone A and D are the correct answers
Which of the following is the name of the compound below? • 2-methyl-5-ethylhexanal • 3-ethyl-6-methylcyclohexanecarbaldehyde • 2-methyl-5-ethylcyclohexanone • 3-ethyl-5-methylcyclohexanone C is the correct answer.
Which compound absorbs at the higher IR frequency? B due to it being unconjugated. A due to ring strain increasing as rings decrease in size.
Three compounds with the formula C4H8O are below. Compound A has 3 peaks in the C-13 NMR. Compound B has a signal at 9.8 ppm in the proton NMR. Compound C has a singlet at 2.1 ppm. Label the compounds below with the correct letter. c B A
Reactions of Aldehydes and Ketones—General  Reaction at the carbonyl carbon—the elements of H and Nu are added to the carbonyl group.  Reaction at the carbon.