Organic Chemistry 2 Final Exam Review

The paragraph introduces an organic chemistry practice session focusing on multiple-choice questions. The first question discusses the oxidation of an aldehyde to a carboxylic acid using silver oxide as the reagent. It explains the specificity of the Tollens' reagent for aldehydes and alpha-hydroxy ketones. The second question explores a radical bromination reaction involving ethyl isopropyl benzene, highlighting the selectivity for tertiary carbon due to the stability of the tertiary radical formed. The summary also reviews different reactions involving bromine, such as radical bromination of alkanes and alkenes, and the anti-Markovnikov addition in the presence of peroxides.

This section delves into the comparison of hydrogen acidity in various organic compounds, focusing on the impact of alpha hydrogens adjacent to carbonyl groups and the influence of electron-donating and electron-withdrawing groups on pKa values. It explains why carboxylic acids are more acidic than other compounds mentioned, with a typical pKa range of four to five. The paragraph emphasizes the general trend of increasing acid strength moving down and to the right on the periodic table and notes exceptions to these trends.

The paragraph discusses the use of IR spectroscopy for identifying functional groups in organic compounds. It describes the characteristic IR spectrum peaks for carboxylic acids, including the broad OH stretch and carbonyl stretch, and uses these to eliminate incorrect structures in a multiple-choice question. The summary also touches on the distinction between alcohol and carboxylic acid peaks and the importance of recognizing sp2 and sp3 hybridized carbons in the CO stretch region.

This section outlines the process of synthesizing para-nitro benzoic acid from benzene, discussing the importance of the relative positions of the nitro and carboxylic acid groups. It analyzes various reaction pathways, including nitration, methylation, and oxidation steps, and explains why certain pathways lead to the meta rather than the desired para product. The correct method involves initial photochemical alkylation, followed by nitration and oxidation to achieve the target molecule.

The paragraph examines different reagents used to convert an acid chloride into an ester. It dismisses reagents that would produce alcohols or ketones and identifies alcohol as the correct reagent for this transformation. The summary includes a brief explanation of the mechanisms involved in the reactions with Gilman reagent and alcohol, highlighting the formation of tetrahedral intermediates and the final products.

This section provides a detailed explanation of the Wittig reaction, which converts ketones into alkenes. It describes the initial formation of a phosphonium ion by the nucleophilic attack of triphenylphosphine on an alkyl halide, followed by the reaction with a ketone to form an alkene. The summary includes the mechanism of the reaction, the formation of a betaine intermediate, and the final product, triphenylphosphine oxide.

The paragraph focuses on the Diels-Alder reaction, a cycloaddition process that forms six-membered rings. It discusses the criteria for selecting the correct diene and dienophile, emphasizing the need for a conjugated diene and an electrophile with a double bond. The summary includes the elimination of incorrect choices based on carbon atom count and the presence of a bicyclic compound in the product, leading to the identification of the correct answer.

This section explains the intramolecular aldol reaction, which involves the formation of a six-membered ring through the reaction of a diketone with sodium hydroxide and heat. The summary details the mechanism of the reaction, including deprotonation to form a carbanion, nucleophilic attack on the carbonyl carbon, and the subsequent dehydration step that leads to the formation of an alpha,beta-unsaturated ketone.

The paragraph explores the concepts of kinetic and thermodynamic control in organic reactions, specifically when adding a methyl group to a cyclohexanone. It discusses the influence of the base used (LDA or NaH) and the reaction temperature on the formation of kinetic versus thermodynamic products. The summary explains the preference for the kinetic product at low temperatures with LDA as the base, and the mechanism of the reaction is also outlined.

This section discusses the Fries and Wolff-Kishner reductions, which convert aromatic ketones to methylene groups (CH2) on the aromatic ring. The summary explains the mechanism of the Fries reaction, involving the initial acylation of the aromatic ring followed by reduction with hydrazine and potassium hydroxide. It also touches on the regioselectivity of the bromination step, influenced by the electron-donating effects of the oxygen and propyl groups.

The paragraph examines the use of NMR spectroscopy to determine the number of distinct hydrogen signals in various organic compounds. It explains how to analyze the symmetry and electronic environment of hydrogen atoms to predict the number of signals observed. The summary includes the process of elimination based on the number of signals and concludes with the identification of compounds that show two signals in an NMR spectrum.

This section explores the reactions between ketones and amines, leading to the formation of imines or enamines. It discusses the nucleophilic attack of a primary amine on a ketone to form an imine and the reaction of a secondary amine to form an enamine. The summary differentiates between the two types of reactions based on the nature of the amine and the stability of the resulting alkene.

The paragraph delves into the concept of aromaticity in organic chemistry, as defined by Huckel's rule, which requires a compound to have 4n+2 pi electrons for aromaticity, where n is a positive integer. It examines the structure of various compounds, including pyrrole and furan, to determine if they are aromatic based on the presence of conjugated pi electrons and planarity. The summary identifies a compound with six pi electrons and an sp3 hybridized carbon, which disrupts the conjugation and planarity required for aromaticity.

This section uses H NMR spectroscopy to analyze the structure of an organic compound with signals corresponding to an aldehyde, ester, ether, and benzene ring. The summary involves the elimination of incorrect structures based on the absence of certain signals and the analysis of chemical shifts and splitting patterns to match the correct compound. It concludes with the identification of the correct structure based on the NMR data provided.