ochem2 week 10 part 1
Naming Nitriles
Nitriles discussed as a new topic in nomenclature.
Definition of Nitriles: Organic compounds containing a cyano (-C≡N) group.
Three scenarios outlined in the textbook for naming nitriles.
Emphasis on the first carbon of the nitrile defining the compound’s name.
Naming Rules
When nitrile carbon is position 1:
Name the compound using standard IUPAC rules and add "nitrile".
Example: 4-methylpentane nitrile when the cyano group is at one position.
When nitrile carbon is not position 1:
Treat as a substituent and name it as "cyano".
Example: 4-cyanobutanoate if cyano is not at the principal position.
Additional Naming Groups
Esters:
Named using the suffix "oate".
Thioesters: Mention of replacing "oate" with "thioate" in the presence of sulfur.
Acyl Phosphates: Niche group not frequently encountered.
Named after the attached groups followed by "phosphate".
Example showing how more complex groups can add nuance to naming.
Reactions in Organic Chemistry
Transition into describing reaction mechanisms, particularly involving nucleophiles and electrophiles.
Emphasis on the relevance of Grignard reagents and their contextual application in organic reactions.
Distinction made between the nucleophilic acyl substitution and Grignard reaction sequences.
Grignard Reaction with Esters
Mechanism Steps:
Grignard reagent attacks the carbonyl carbon of the ester.
The pi bond breaks, and a leaving group departs.
The negative charge is stabilized internally leading to product formation.
Emphasizes the importance of understanding this fundamental sequence as a cornerstone of organic reactivity.
Nucleophilic Acyl Substitution
Outline of the nucleophilic acyl substitution mechanism:
Attack the carbonyl carbon by the nucleophile.
Formation of a tetrahedral intermediate.
Departure of the leaving group.
Regeneration of the carbonyl group and protonation, leading to the final product.
Reactivity of Acid Derivatives
Discusses reactivity differences of functional groups derived from carboxylic acids:
The most reactive derivative: Acid Chlorides.
Followed by Anhydrides, Esters, Thioesters, and finally Amides (least reactive).
Principle of Reactivity: More unstable leaving groups yield faster reactions due to more favorable bond dissociation energy.
Examples illustrating transformation potential among derivatives (e.g., converting acid chlorides to esters).
Chart of Derivative Reactivity
Acid Chloride: Most reactive, high reactivity due to poor leaving group stability.
Anhydride: Moderately reactive with resonance stabilization.
Ester: Better leaving group than amides due to electron-withdrawing from oxygen.
Amide: Least reactive due to resonance stability.
Synthesis of Anhydrides
Effective methods outlined:
Heating carboxylic acids requires extreme conditions; not practical.
Reacting acid chlorides with carboxylic acids is preferred at lower temperatures using base catalyst.
Importance of catalyst noted, with examples of pyridine and triethylamine.
Mechanism Practice
Challenges identified in understanding mechanisms of reaction, particularly with unconventional steps (like using the carbonyl oxygen).
Encourage visualizing mechanisms to aid understanding.
Reactions involving different nucleophiles lead to distinct products, with suggested exercises for clarity.
Formation of Esters via Fischer Esterification
Utilizing a combination of carboxylic acid and alcohol.
Requires strong acid catalyst (commonly sulfuric acid).
Mechanism explained in relation to nucleophilic attack and elimination.
Protonation and its effects on electrophilicity.
Summary
Concludes with an affirmation of the goals to understand complex reactions and stress practice in naming and mechanisms.
Engage with exercises for further reinforcement of concepts discussed.