OChem Notes: Functional Groups, Alcohols, Amines, Aldehydes, Ketones, Carboxylic Acids, and VSEPR

  • Course context and logistics
    • 48 hours to complete an upcoming assignment
    • First take-home quiz available Monday, due Wednesday
    • Course focus today is OCAM (organic chemistry, arithmetic of mechanisms) with some Gen Chem review
    • Emphasis on identifying functional groups for reactions and nomenclature
  • Functional groups: purpose and importance
    • Functional groups are groups of atoms within molecules that impart characteristic reactivity
    • They behave similarly across different molecules, enabling generalizations about reactions
    • They largely determine nomenclature: naming priority often follows the presence of a functional group
  • Alcohols: the OH functional group (hydroxyl) attached to carbon
    • An alcohol contains a hydroxyl group OH bound to a carbon atom
    • Difference from generic OH⁻ in water/base context: in alcohols, the OH is bonded to a carbon
    • Visual identification: must have a C–OH bond (not just OH by itself)
    • Common examples: ethanol (drinking alcohol) and isopropyl alcohol
    • Condensed vs fully condensed structures for ethanol
    • Condensed: extCH<em>3−extCH</em>2−extOHext{CH}<em>3- ext{CH}</em>2- ext{OH}
    • Fully condensed structural: extCH<em>3extCH</em>2extOHext{CH}<em>3 ext{CH}</em>2 ext{OH} (no lone pairs shown in condensed form)
    • Alcohols can be primary, secondary, or tertiary depending on the carbon attached to the OH
    • How to classify: look at the carbon directly bonded to the OH; count how many different carbons that carbon is attached to
    • Examples of classification
    • Ethanol: the carbon attached to OH is connected to one other carbon → primary alcohol
    • A secondary alcohol example (from class discussion): the carbon attached to the OH is connected to two carbons → secondary alcohol
    • Alkyl halide (alkyl halide) example for contrast
    • If a halogen attaches to a carbon, classify by how many carbons that carbon is attached to
    • Tertiary alkyl halide example: a carbon bonded to three carbons plus a halogen
    • Practice thought: given a structure, identify whether the alcohol is primary, secondary, or tertiary by examining the carbon bonded to OH
    • Alcohols and stability in reactions: primary < secondary < tertiary for carbocation formation in SN1/SN2 contexts (concept preview)
  • Practice task from lecture on alcohols
    • Draw four alcohols with molecular formula extC<em>4extH</em>10extOext{C}<em>4 ext{H}</em>{10} ext{O} and classify each as primary, secondary, or tertiary
    • Approach used in lecture:
    • Start with four carbons connected in a chain
    • Ensure exactly one COH unit (one OH attached to a carbon)
    • Fill hydrogens to satisfy valence (C forms 4 bonds, O forms 2 bonds, etc.)
    • Determine the type by examining the carbon attached to OH
    • Example conclusions from the session: several distinct alcohol structures exist with the same formula; different arrangements yield primary or secondary classifications depending on the immediate carbon bonded to OH
  • Amines: nitrogen-containing functional group
    • An amine is a nitrogen atom bonded to one, two, or three different carbons
    • Amine classification by substitution on nitrogen: primary (one carbon substituent, two hydrogens), secondary (two carbon substituents, one hydrogen), tertiary (three carbon substituents, no hydrogens)
    • Basic amine examples:
    • Ammonia (NH₃) is the simplest precursor with no C–N bonds highlighted
    • After substitution of hydrogens with carbon groups, you get amines
    • Examples discussed:
    • Methylamine: extCH<em>3extNH</em>2ext{CH}<em>3 ext{NH}</em>2 (primary amine)
    • Dimethylamine: ext(CH<em>3)</em>2extNHext{(CH}<em>3)</em>2 ext{NH} (secondary amine)
    • Trimethylamine: ext(CH<em>3)</em>3extNext{(CH}<em>3)</em>3 ext{N} (tertiary amine)
    • Rule of thumb: classify by how many different carbons are directly bonded to the nitrogen
  • Aldehydes and ketones: carbonyl-containing groups
    • Carbonyl group is a carbon double-bonded to oxygen (C=O)
    • Aldehydes vs ketones differ by what is attached to the carbonyl carbon
    • Aldehyde: carbonyl carbon bonded to at least one hydrogen (R–CHO or H–C=O–R)
      • Formaldehyde: extH2extC=Oext{H}_2 ext{C=O} (simplest aldehyde)
      • Acetaldehyde: extCH3extCHOext{CH}_3 ext{CHO} (example of aldehyde with one carbon substituent)
    • Ketone: carbonyl carbon bonded to two carbons (R–CO–R') and has no hydrogens on the carbonyl carbon
      • Acetone: extCH<em>3extCOCH</em>3ext{CH}<em>3 ext{COCH}</em>3 (common ketone)
    • Important concept: aldehydes can have one or two hydrogens on the carbonyl carbon; ketones have zero hydrogens on that carbon
    • For the assignment: draw condensed structures for three ketones with the molecular formula extC<em>5extH</em>10extOext{C}<em>5 ext{H}</em>{10} ext{O}
    • Example ketones (three valid structures with C5H10O):
      • 2-pentanone: extCH<em>3−extCO−extCH</em>2−extCH<em>2−extCH</em>3ext{CH}<em>3- ext{CO}- ext{CH}</em>2- ext{CH}<em>2- ext{CH}</em>3
      • 3-pentanone: extCH<em>3−extCH</em>2−extCO−extCH<em>2−extCH</em>3ext{CH}<em>3- ext{CH}</em>2- ext{CO}- ext{CH}<em>2- ext{CH}</em>3
      • 3-methyl-2-butanone: extCH<em>3−extCO−extCH(extCH</em>3)−extCH3ext{CH}<em>3- ext{CO}- ext{CH}( ext{CH}</em>3)- ext{CH}_3
    • Note: ketones do not come in primary/secondary/tertiary classifications; the carbonyl carbon is always bonded to two carbons
  • Carboxylic acids: carbonyl with hydroxyl
    • Carboxyl group pattern: a carbon double-bonded to oxygen and also bonded to a hydroxyl group (COOH or CO2H)
    • Common example: acetic acid (ethanoic acid): extCH3extCOOHext{CH}_3 ext{COOH}
    • Alternative representation: extCOOHext{COOH} or extCO2extHext{CO}_2 ext{H} depending on drawing convention
    • Carboxylic acids are defined by the pattern: a carbonyl (C=O) with an OH on the same carbon
    • The discussion also noted that replacing the OH H with a carbon substituent leads to amide-like structures (e.g., R–CO–NR'R''), illustrating functional group interconversion possibilities, though the focus here is on acid functionality
  • Three-dimensional structure and VSEPR (shape prediction)
    • Key questions for a given region of a molecule:
    • How many lone pairs are around the central atom?
    • How many bonding directions (distinct regions of electron density) are around the atom?
    • Electron pair geometry vs molecular geometry
    • Electron pair geometry: predicted shape based on electron density (lone pairs + bonds)
    • Molecular geometry: the actual arrangement of atoms in space
    • VSEPR theory (Valence Shell Electron Pair Repulsion): used to predict shapes
    • Examples:
    • Methane (CH₄): zero lone pairs on carbon; four bonding directions; electron geometry = molecular geometry = tetrahedral; predicted bond angle ≈ 109.5exto109.5^ ext{o}
    • Ammonia (NH₃): one lone pair on N; three bonding directions; electron geometry = tetrahedral, molecular geometry = trigonal pyramidal; predicted bond angle < 109.5exto109.5^ ext{o} (approximately 107.3exto107.3^ ext{o})
    • Water (H₂O): two lone pairs on O; two bonding directions; electron geometry = tetrahedral; molecular geometry = bent (angular); bond angle ~ 104.5exto104.5^ ext{o}
    • Formaldehyde (H₂C=O): carbonyl carbon has zero lone pairs; three bonding directions around carbonyl carbon (the C=O counts as one direction, plus two C–H bonds); about 120exto120^ ext{o} around that carbon (roughly trigonal planar)
    • Distinguishing electron geometry from observed geometry helps explain deviations from ideal angles
  • Summary of practical takeaway for OChem 1 concepts
    • Identify functional groups by key atom connections (e.g., C–OH for alcohols, C=O for carbonyl-containing groups, C–N for amines, etc.)
    • Use carbon next to OH to classify alcohols as primary, secondary, or tertiary
    • Recognize that aldehydes have at least one H on the carbonyl carbon, while ketones have two carbon substituents and no hydrogens on that carbon
    • For amines, count how many carbons are directly bonded to nitrogen to classify as primary/secondary/tertiary
    • For three-dimensional considerations, apply VSEPR by counting lone pairs and bonding domains to predict electron geometry and molecular geometry, then compare predicted angles with observed values
  • Quick reference formulas (LaTeX-ready)
    • Ethanol: extCH<em>3ext−CH</em>2ext−OHext{CH}<em>3 ext{-CH}</em>2 ext{-OH}
    • Primary alcohol example (ethanol): extCH<em>3extCH</em>2extOHext{CH}<em>3 ext{CH}</em>2 ext{OH}
    • Isopropanol (secondary alcohol): ext(CH<em>3)</em>2extCHOHext{(CH}<em>3)</em>2 ext{CHOH}
    • Methylamine: extCH<em>3extNH</em>2ext{CH}<em>3 ext{NH}</em>2
    • Dimethylamine: ext(CH<em>3)</em>2extNHext{(CH}<em>3)</em>2 ext{NH}
    • Trimethylamine: ext(CH<em>3)</em>3extNext{(CH}<em>3)</em>3 ext{N}
    • Formaldehyde: extH<em>2extC=OextorextCH</em>2extOext{H}<em>2 ext{C=O} ext{ or } ext{CH}</em>2 ext{O}
    • Acetaldehyde: extCH3extCHOext{CH}_3 ext{CHO}
    • Acetone: extCH<em>3extCOCH</em>3ext{CH}<em>3 ext{COCH}</em>3
    • Acetic acid: extCH3extCOOHext{CH}_3 ext{COOH}
    • 2-pentanone: extCH<em>3extCOCH</em>2extCH<em>2extCH</em>3ext{CH}<em>3 ext{COCH}</em>2 ext{CH}<em>2 ext{CH}</em>3
    • 3-pentanone: extCH<em>3extCH</em>2extCOCH<em>2extCH</em>3ext{CH}<em>3 ext{CH}</em>2 ext{COCH}<em>2 ext{CH}</em>3
    • 3-methyl-2-butanone: extCH<em>3extCOCH(CH</em>3)extCH3ext{CH}<em>3 ext{COCH(CH}</em>3) ext{CH}_3
    • Four-carbon secondary amines with formula extC<em>4extH</em>11extNext{C}<em>4 ext{H}</em>{11} ext{N} (three examples):
    • Diethylamine: (extCH<em>3extCH</em>2)2extNH( ext{CH}<em>3 ext{CH}</em>2)_2 ext{NH}
    • N-methylpropylamine: extCH<em>3extNHCH</em>2extCH<em>2extCH</em>3ext{CH}<em>3 ext{NHCH}</em>2 ext{CH}<em>2 ext{CH}</em>3
    • N-methylisopropylamine: extCH<em>3extNHCH(CH</em>3)2ext{CH}<em>3 ext{NHCH(CH}</em>3)_2
  • Quick thoughts on naming priority (recap)
    • Functional group presence often determines the root name and suffix
    • Multiple functional groups in a molecule require prioritization rules (e.g., carboxylic acids often take priority in naming over alcohols or amines)
  • Practice prompts you might see on exams
    • Given a molecule, identify the functional group and classify substituents (primary/secondary/tertiary where applicable)
    • Draw condensed and Lewis structures for given molecular formulas and verify atom counts
    • Predict three-dimensional geometry using VSEPR for a chosen central atom, including identifying lone pairs and bond directions
    • Write three different ketones with formula extC<em>5extH</em>10extOext{C}<em>5 ext{H}</em>{10} ext{O} and explain why aldehyde/ketone distinctions matter (carbonyl carbon attachments)
  • Note on style and symbols
    • All chemical formulas and equations are shown in LaTeX format for clarity where appropriate, enclosed in double dollar signs
    • Relations to broader OChem concepts (SN1/SN2/E1/E2, Markovnikov’s rule, carbocation stability) are introduced as a foundation for upcoming topics