Alkynes

nomenclature

  1. the basics - be able to draw a molecule from the name
  2. Reusch (alkenes and alkynes)

Preparation of alkynes

elimination of dihalides

  1. first E-2 easy, second hard (use strong base like sodamide/ high temp)
  2. use geminal or vicinal dihalides
  3. Reusch

addition and SN2 reactions of alkyne salts

  • see below under Reactions of alkynes

Reactions of alkynes

  1. Reusch
  2. NaNH2 (made from Na/NH3 with Fe3+) with terminal alkynes to give salt
  3. Ag+ or Cu+ to precipitates of MCC-R
  4. alkyne salt SN2 reaction with primary alkyl halides and E-2 with secondary and tertiary alkyl halides
  5. alkyne salt addition to ketones and aldehydes to give alcohols
  6. reduction with H2/Pt or Pd catalysts to alkane
  7. reduction with H2/Lindlar's catalyst to cis alkene
  8. reduction with Na/NH3 to trans alkene
  9. addition of halogens to trans alkenyl dihalides then vicinal tetrahalides
  10. Markovnikov addition of HBr or HCl to alkenyl halides then geminal dihalides
  11. Markovnikov addition of H2O using Hg++/H2O/H2SO4 to methyl ketones via tautomerism of an enol
  12. Anti-Markovnikov addition of H20 using 1)BH(sia)2 (disiamylborane) 2)H2O2,OH- to aldehydes via tautomerism of an enol
  13. Anti-Markovnikov addition of HBr using HBr/a peroxide to an alkenyl halide then a geminal dihalide
  14. Cold dilute permanganate to diketones
  15. Hot concentrated permanganate to cleave alkyne bond then oxidize to carboxylic acids (or CO2 for terminal alkynes)
  16. Ozonolysis to cleave alkyne bond to carboxylic acids
  17. migration of triple bond to terminal alkyne using hot NaNH2
  18. migration of triple bond to more stable internal alkyne (if there is one) using hot KOH

Practice Problems


click on images below to view solutions

Problem alkyne-1

orgo003.JPG

Problem alkyne-2

alkyne2-1.JPG

Alcohols

Nomenclature

  • the basics - be able to draw a molecule from the name
  • Reusch

Preparation

  1. hydrolysis of alkyl halides with hydroxide
  2. Markovnikov addition of water on alkenes using acid/water (watch for rearrangment of carbocation)
  3. Markovnikov addition of water on alkenes using 1) Hg(OAc)2 2) NaBH4 (oxymercuration - demercuration)
  4. Anti-Marknovnikov addition of water on alkenes using 1) BH3 2) NaOH, H2O2 (hydroboration - oxidation)
  5. hydroxylation of alkenes to syn glycols using cold dilute permanganate or OsO4, or anti glycols using peracids with aqueous acids Reusch 5i>
  6. Reduction of aldehydes and ketones with NaBH4 or LiAlH4
  7. Reduction of esters or carboxylic acids with LiAlH4 (NaBH4 does not react)
  8. Reduction of aldehydes and ketones with Raney Ni (also reduces alkenes)
  9. synthesis of tertiary alcohols from Grignard or organolithium reagents with esters, acid chlorides or ketones UCalgary
  10. synthesis of secondary alcohols from Grignard or organolithium reagents with aldehydes
  11. synthesis of primary alcohols from Grignard or organolithium reagents with formaldehyde or ethylene oxide
  12. remember that Grignard or organolithium reagents react with even weak acids (terminal alkynes, alcohols, thiols, carboxylic acids, etc.) to replace the metal with H
  13. thiols (R-SH) prepared by adding excess NaSH to alkyl halides or tosylates

Reactions

  1. dehydration to alkenes using a strong acid (e.g. H2SO4) via E-1, watch out for 1,2 shifts (can use reduction of alkene with Pd/H2 as a 2 step route from alcohols to alkanes)
  2. oxidation of primary alcohols to aldehydes via PCC (secondary alcohols go to ketones also but cheaper reagents can be used)
  3. oxidation of primary alcohols to carboxylic acids and secondary alcohols to ketones via general pupose oxidizers (e.g. CrO3, KMnO4, NaCr2O7)
  4. ROH to RCl using SOCl2 for primary and secondary alcohols (SOCl2 without base gives retention of chirality via SNi mechanism) Wikipedia
  5. ROH to RCl using PCl3 for primary and secondary alcohols (inversion of chirality SN2)
  6. ROH to RBr using PBr3 for primary and secondary alcohols (inversion of chirality SN2)
  7. ROH to RBr using HBr for tertiary alcohols (SN1)
  8. ROH to RI using P/I2 for primary or secondary alcohols
  9. ROH to RBr using HBr for secondary and tertiary alcohols (via SN1)
  10. ROH to RCl using HCl/ZnCl2 fastest for tertiary alcohols and slow with secondary alcohols (SN1) Lucas test
  11. ROH to esters using acid chlorides (better) or mixing alcohol and carboxylic acid with acid catalyst and removing water
  12. ROH and H3PO4 (phosphoric acid) heat to make some phosphate esters (e.g. trimethyl phosphate) - most alcohols will undergo E-1 and dehydrate to alkenes, as described above
  13. ROH and HNO3 (nitric acid) to make nitrate esters (explosive, e.g. nitroglycerin)
  14. ROH to ROTs (tosylates) using TsCl, useful for doing SN2 reactions from primary alcohols:
  15. ROTs to RH using LiAlH4 (another way to go from alcohol to alkane in 2 steps)
  16. ROTs to RNH2 using ammonia
  17. ROTs to ROH using hydroxide
  18. ROTs to RX using halide salt (F-,Cl-,Br-,I-)
  19. ROTs to RCN (nitrile or cyanide) using NaCN
  20. with NaH, Na (primary or secondary alcohols) or K (for tertiary alcohols) to generate alkoxides
  21. phenols are much more acidic than aliphatic alcohols (phenolates can be made with hydroxide, electronegative groups make more acidic) Reusch
  22. Williamson ether synthesis (alcoxide with primary alkyl halides or tosylates, secondary or tertiary give E-2)
  23. tertiary glycols undergo pinacol rearrangement
  24. glycols are converted to aldehydes or ketones using periodic acid (HIO4), thus hydroxylation then HIO4 is an alternative to straight ozonolysis of alkenes
  25. Thiolates are more nucleophilic and less basic than alcoxides so can do SN2 with primary or secondary alkyl halides and tosylates (tertiary give E-2) Reusch
  26. thiols oxidized by KMnO4, HNO3 to sulfonic acids (R-SO3H)
  27. thiols oxidized by Br2 to disulfides (R-SS-R), also used by proteins

Practice Problems



TEST 1


Infrared Spectroscopy (IR)

  • Reusch
  • measures the bending and stretching of bonds
  • higher wavenumber (in cm^-1) corresponds to higher energy
  • heavier atom gives lower energy and lower wavenumbers
  • higher bond energies (e.g. single -> double -> triple bonds) give higher wavenumbers
  • useful range 1600-3500 cm^-1 (any absorptions below that are in the fingerprint region)
  • C=C unconjugated alkene 1640-1680
  • C=C conjugated alkene 1620-1640
  • C=C aromatic 1600
  • C-H (sp3) 2900-3000
  • C-H (sp2) 3000-3100
  • C-H (sp) 3300
  • hydrogen bonded N-H, O-H broad near 3300, CO2H very broad 2500-3500
  • C=O ketone, aldehydes, carboxylic acids 1710
  • C=O conjugated ketone or aldehyde 1680
  • C=O esters 1730-1740
  • C=O amides 1640-1680
  • C=O acid chlorides 1780
  • C=O cyclobutanones 1780
  • C-H aldehyde 2700 and 2800
  • C=N 1660
  • CN (nitrile) 2250
  • CC alkyne 2150

Mass Spectrometry (MS)

  • Reusch
  • molecules acquire a charge then are separated by mass in the mass spectrometer by moving in a magnetic field
  • M+ is molecular ion peak
  • base peak is the strongest peak
  • high resolution MS can give elemental analysis because atoms have non integer masses
  • C-13 is about 1%, thus there will be a small M+1 peak
  • for methyl M-15, ethyl M-29, propyl M-43, butyl M-57
  • for Br M+2 = M+
  • for Cl M+2 = 1/3 M+
  • for N, M+ is odd
  • for S M+2 = 4% M+
  • alcohols that can dehydrade often M+ not seen, only M-18
  • break C-C bonds to form stable carbocations (tertiary, benzylic, allylic)

Nuclear Magnetic Resonance Spectroscopy (NMR)

  • Reusch
  • can view every H and C in molecules as peaks
  • scale in ppm (delta scale), relative to tetramethylsilane (TMS), defined as zero
  • in a typical NMR plot, higher ppm are on the left (low field, more deshielded)
  • integration corresponds to number of Hs
  • electronegative elements deshield
  • adjacent and non-equivalent (2-3 bonds) H's couple with each other and split peaks (N+1 rule), giving coupling constant J
  • J for alkenes: cis 10 Hz, trans 15 Hz, geminal 2 Hz
  • J for aromatics: ortho 8 Hz, meta 2 Hz
  • CH2 next to chiral center are diastereotopic and the H's are not equivalent
  • alkanes 0.9-1.5 ppm
  • aromatics 7-8 ppm
  • alkenes 5-6 ppm
  • aldehydes 9-10 ppm
  • terminal alkyne H 2.5 ppm
  • benzylic or next to ketone or aldehyde 2.1 - 2.3 ppm
  • CH2-X (X = O,N,halogen) 3 - 4 ppm
  • carboxylic acid 10-12 ppm, although may be very broad
  • amine and alcohols may be broad, very variable and not undergo 3 bond coupling
  • in ultrapure samples, H of OH may exhibit 3 bond coupling and splitting
  • hydrogen bonding H's can be replaced with H NMR invisible D's by adding D2O or CD3OD
  • C NMR do not show C-C coupling because only about 1% of C's are C-13
  • C NMR are usually proton spin decoupled so that only singlets are obtained
  • C NMR shifts: carbonyl 160-210 ppm, aromatic 100-150 ppm, alkynes 75-95 ppm, alkanes 0-35 ppm

Problems


nmr1.JPG
nmr3.JPG

Ethers

  • UCalgary
  • R-O-R
  • nomenclature - be able to draw molecule from name - note special names for epoxides
  • somewhat polar but bp close to alkanes
  • can solvate cations and form complex with Grignard reagents
  • hydrogen bond acceptor but not a donor
  • cyclic ethers: epoxides (oxiranes), oxetanes, furans, THF (tetrahydrofuran) is common solvent

synthesis

  • Williamson ether synthesis
  • Alkoxymercuration-demercuration of alkenes using 1) Hg(OAc)2, ROH 2) NaBH4 (Markovnikov addition of an alcohol)
  • Dehydration of alcohols using strong acid (e.g. H2SO4) poor method because competing E-1
  • epoxides from alkenes and peracid (e.g. MCPBA)
  • epoxides from cyclization of halohydrin (H2O, Cl2, NaOH)

reactions

  • with HI and HBr to cleave and give 2 alkyl halides (aromatic ethers stop at phenol stage)
  • with oxygen to give explosive hydroperoxides
  • epoxides open in base with nucleophile attacking sterically less hindered side (e.g. alkoxide, Grignard)
  • epoxides open in acid with nucleophile attacking sterically more hindered side (e.g. alcohol)

Sulfides

  • nomenclature: thiols, thioethers, sulfides
  • RSH more acidic than alcohols (similar to phenols)

Reactions

  • thiolates react with primary or secondary alkyl halides (or tosylates) to give thioethers (with tertiary would give E-2)
  • thioethers react with H2O2 to give sulfoxides then sulfones

Synthesis

  • thiols can be made with alkyl halides (or tosylates) with excess NaSH

Ultraviolet Spectroscopy

  • the more extended the conjugation the longer the wavelength (lower the energy) of absorption
  • in UV spectra, +30 nm for extending conjugation and +5 for alkyl

Reactions of Conjugated Systems

  • molecular orbitals of allylic and butadiene systems
  • 1,2 and 1,4 addition of HBr or NBS to conjugated dienes
  • SN2 reactions of allylic halides
  • Diels-Alder reaction: diene must be s-cis, endo rule, stereospecificity (avoid 1,3 relationship of D and W)
  • cycloadditions [2 + 2] thermally disallowed but photochemically allowed
  • cycloadditions [4 + 2] thermally allowed but photochemically disallowed

Aromatic compounds

  • aromaticity adds stability beyond just conjugation
  • required for aromaticity: a complete ring of co-planar p orbitals and 4N + 2 pi electrons
  • required for anti-aromaticity: a complete ring of co-planar p orbitals and 4N pi electrons
  • forming an aromatic structure upon losing a proton leads to high acidity alkanes (e.g. cyclopentadiene)
  • predict weak and strong bases depending on changes in aromaticity
  • nomenclature: ortho, meta, para, phenyl, benzyl