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Organic Chemistry Chapters 22-23

Organic Chemistry Chapters 22-23. Straight Chain Alkanes. An alkane is a saturated hydrocarbond i.e. it has no double bonds, and every carbon has the maximum possible number of hydrogens CH 4 = methane CH 3 CH 4 = ethane CH 4 CH 3 CH 4 = propane CH 4 CH 3 CH 3 CH 4 = butane

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Organic Chemistry Chapters 22-23

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  1. Organic ChemistryChapters 22-23

  2. Straight Chain Alkanes • An alkane is a saturated hydrocarbond • i.e. it has no double bonds, and every carbon has the maximum possible number of hydrogens • CH4 = methane • CH3CH4 = ethane • CH4 CH3CH4 = propane • CH4CH3CH3CH4 = butane • Beyond 4 carbons, standard Greek prefixes are used • E.g. 5C = pentane, 6C = hexane

  3. Branched Chain Alkanes • Identify the main chain. • It will have the highest number of carbon atoms in it • Name the main chain using standard conventions • Number the carbons in the main chain from left to right • Identify which carbon the secondary chain branches from • Identify the number of carbons in the secondary chain • Name the secondary chain • The final name is the number you identified in step 4, followed by the name of the secondary chain with the ending –yl, followed by the name of the main chain. • E.g. 2-methylpropane indicates is the name for the molecule

  4. Cycloalkanes • Identify the number of carbons in backbone of the ring. • Use the carbon number to name the ring, adding the prefix “cyclo” to indicate that it is a ring • E.g. the smallest ring possible is cyclopropane, which has 3 carbons in the main ring • Number the carbons in the main ring, starting at the top and working clockwise. • If any substituent groups branch off the main ring, identify which number carbon the branch from • Name the substituent group, remembering to add the suffix –yl to the stem • The final name is the number you identified in step 3, followed by the name of the secondary chain with the ending –yl, followed by the name of the main ring. • E.g. 2-methylcyclopropane indicates is the name for the molecule

  5. Alkenes • An alkene is unsaturated because it contains at least C-C double bond. • i.e. it does not contain the maximum number of hydrogen atoms around every carbon atom • Use the same naming convention as alkanes, but use the ending –ene instead of –ane. • Also, by numbering the carbons, indicate the number of the first C in the C-C double bond. • So, 2-butene is the name of the molecule below. • N.B. Because there must be a C-C double bond, the smallest possible alkene is ethene.

  6. Branched-Chain Alkenes • Number the carbons in order to give the lowest number possible to the carbon containing the double bond. • Identify the carbons with substituents attached. • Identify the substituents. • See page 713, problem 22-3 for an example

  7. Alkynes • Alkynes have at least one C-C triple bond, and are therefore also unsaturated. • Alkynes use the same naming conventions as alkenes, but use the –yne ending instead of –ene.

  8. Isomers • Isomers have the same molecular formula, but look different. • Structural isomers are bonded in different orders. • E.g. pentane, 2-methylbutane, and 2,2-dimethylpropane are all C5H12 molecules, but they have 5, 4, or 3 carbons in their main chains, respectively, and 0, 1, or 2 methyl substituent groups, respectively. • Stereoisomers have the same bonding order, but are arranged differently in space. Stereoisomers are designated cis- or trans-. • Optical isomers have the same bonding order, but exhibit chirality. This means that they are mirror images of each other and bend light clockwise (D-isomers) or counterclockwise (L-isomers)

  9. Aromatic & Aliphatic Hydrocarbons • Aromatic ring • An exceptionally stable planar ring of atoms with resonance structures that consist of alternating double and single bonds, e. g. benzene: • Aromatic compound • A hydrocarbon compound containing an aromatic ring. • Aromatic compounds have strong, characteristic odors. • Aliphatic Hydrocarbons • A hydrocarbon compound lacking a ring structure

  10. Carcinogens • Carcin= cancer • Gen= create • A carcinogen, therefore, causes cancer • Many of the aromatic compounds are known carcinogens, others are suspected.

  11. Fractionating Petroleum • All aromatic and aliphatic compounds are currently obtained from fossil fuels • The most common source of hydrocarbons is petroleum • Raw petroleum has > 1000 different compounds in it and is called crude oil • It is therefore separated via fractional distillation into its simpler components. • Industry can then take the simpler components to create gasoline, plastics, shampoos, contact lenses, and the wide variety of other hydrocarbon-based consumer products that all originate from petroleum.

  12. Functional Groups • A functional group in an organic molecule is an atom or molecule that always reacts in a predictable manner • The addition of functional groups to a basic hydrocarbon always produces a substance with distinct properties from the basic hydrocarbon

  13. Halides • Halides • Any of the Group 7A elements that are attached to a hydrocarbon • Alkyl halides are organic compounds containing a halogen covalently bonded to an aliphatic carbon atom • Aryl halides are organic compounds containing a halogen covalently bonded to an aromatic carbon atom • 1. The simplest halogenoalkane is exemplified by chloromethane (methyl chloride) • 2. to 7. Are examples of multi-substituted halogenoalkanes based on methane … • 2. trichlorofluoromethane, (CFC-11, a chlorofluorocarbon or CFC) • 3. dichlorodifluoromethane, (CFC-12) • 4. difluoromethane (a hydrofluorocarbon or HFC, methylene difluoride) • 5. tribromomethane • 6. tetrachloromethane, (carbon tetrachloride) • 7. chlorodifluoromethane, (HCFC-22 a hydrochlorofluorocarbon or HCFC)

  14. Carboxylic Acids • The primary suffix name for a carboxylic acid is based on the "longest carbon chain name *" + "oic acid" for the COOH acidic bond system • methanoic acid (formic acid): • HCOOH • ethanoic acid (acetic acid): • CH3COOH • Propanoic acid (propionic acid): • CH3CH2COOH

  15. Alcohols • Alcohols have the hydroxy group OH attached to at least one of the carbon atoms in the chain. • If the OH group is directly attached to a benzene ring , it is classified as a phenol. • The primary suffix name is ..ol for alcohol and so for the longest carbon chain (alkanol) the names are based on: • 1 carbon, methanol; • 2 carbons, ethanol; • 3 carbons, propanol; • 4 carbons, butanol, etc. • The positions of the substituent alkyl (or other) groups are denoted by using the lowest possible numbers for the associated carbon atoms in the main chain. • If there is more than one 'type' of substituent eg using the prefixes: methyl… and ethyl.. etc., they are written out in alphabetical order (di, tri are ignored in using this rule).

  16. Alcohol Classification • Alcohols are classified according to the atoms/groups attached to the carbon of the hydroxy group • Primary alcohols have the structure R-CH2-OH, R = H, alkyl, aryl etc. ie apart from methanol they have one alkyl/aryl group attached to the C of the C-OH group. • Secondary alcohols have the structure R2CH-OH, R = alkyl or aryl etc. ie they have two alkyl/aryl groups attached to the C of the C-OH group. • Tertiary alcohols have the structure R3C-OH, R = alkyl or aryl etc. ie they have three alkyl/aryl groups attached to the C of the C-OH group. • Ethers are named on the basis of the longest carbon chain with the O-R or alkoxy group, eg methoxy CH3O- or ethoxy CH3CH2O- etc. treated as a substituent group. • Diol, triol and Cycloalcohol (cycloalkanols) structures and names are on a separate web page • Some 'old' names are quoted in () though their use should be avoided if possible [but many still used - just put one into GOGGLE!].

  17. Alcohol Examples • Methanol • CH3OH • Ethanol • CH3CH2OH • Propan-1-ol • CH3CH2CH2OH • Propan-2-ol • CH3CH(OH)CH3

  18. Ethers • Ethers are formed from the condensation of 2 alcohols • R-OH + R'-OH = R-O-R' + H2O • This is called a dehydration synthesis reaction • N.B. R and R' represent organic groups. • Methoxymethane (methyl ether) • CH3OCH3 • Ethoxyethane (ethyl ether) • CH3CH2OCH2CH3

  19. Esters • An ester is a compound formed from an acid and an alcohol . • In esters of carboxylic acids , the -COOH group of one hydrocarbon and the -OH group from another hydrocarbon lose a water and become a -COO- linkage: • R-COOH + R'-OH = R-COO-R' + H2O

  20. Primary and Secondary Amines • An amine is an organic compound that contains a nitrogen atom bound only to carbon and possibly hydrogen atoms. • Primary Amines:  these have two hydrogen atoms and one alkyl or aryl group attached to the nitrogen to form the amine or amino group -NH2. • Methylamine • CH3NH2 • 2-aminopropane • CH3CH(NH2)CH3 • Secondary Amines: these have one hydrogen atom and two alkyl or aryl groups attached to the nitrogen • Dimethylamine • (CH3)2NH • Ethylpropylamine • Diphenylamine

  21. Tertiary Amines • Tertiary amines have no hydrogen atom and three alkyl or aryl groups attached to the nitrogen • Trimethylamine • Ethyldimethylamine • N,N-dimethylphenylamine

  22. Carbonyl Compounds • Aldehydes and ketones are a group of compounds containing the carbonyl group, C=O. • Aldehydes always have a hydrogen atom attached to the carbon of the carbonyl group, so the functional group is -CHO (see diagram above). • The functional group is shown by using 'al' in the suffix part of the name eg methanal, ethanal, propanal etc. • Ketones always have two carbon atoms attached to the carbon atom of the carbonyl group, so the functional group is C-CO-C (see diagram above). • The functional group is shown by using 'one' in the suffix part of the name • eg propanone, butanone, hexan-3-one etc. • The substituent numbers are based on giving the C=O carbon the lowest number • eg 2-methylbutanal ('al' position = 1). • The number position of the C=O group in ketones needs to be specified for carbon chains of over 4, or less, if substituents are present • eg 3-methylbutan-2-one, heptan-2-one, heptan-3-one and heptan-4-one (there is no heptan-1-one, this is heptanal!). • For the same 'carbon number', aldehydes and ketones are structural and functional group isomers : CnH2nO.

  23. Aldehyde Examples • Methanal (formaldehyde) • HCHO • Ethanal (acetaldehyde) • CH3CHO • 2-methylpropanal • CH3CH(CH3)CHO

  24. Ketone Examples • Propanone (acetone) • CH3COCH3 • Butanone (methyl ethyl ketone) • CH3COCH2CH3 • 1-Phenylethanone

  25. Amides • An amide is an organic compound that contains a carbonyl group bound to nitrogen, also known as an acid amide. • Naming: The primary suffix name for an amide is based on the "longest carbon chain name" + "amide" for the CONH2 bond system eg methanamide, ethanamide etc. • Methanamide (formamide) • HCONH2 • Ethanamide (acetamide) • CH3CONH2 • Benzenecarboxamide (benzamide) • C6H5CONH2

  26. Doc Brown’s Web Site • http://www.wpbschoolhouse.btinternet.co.uk/page04/page04.htm

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