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Lecture 4,5,6

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Organic Compounds

Classification of Organic Compounds

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Alkanes

- Contain only C and H

- Form only single bonds

- Basic skeleton to which we add functional groups

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Naming Alkanes

- ends in -ane

- IUPAC

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Cycloalkanes

- Hydrocarbons can form cyclic structures

- are named by adding cyclo- before the name of the alkane chain with the same number of C atoms

Isomers

- Alkanes with 4 of more Cs can be rearranged

- Can have a subgroup attached to the C

- Can have more than one chemical formula

- Same molecular formula, different arrangements 

- Ex. C5H12

- The groups that branch from alkanes are called alkyl groups

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Methyl group on the second carbon

2 Methyl groups on the second carbon

Alkyl Groups

- Alkanes that are missing one H

- Substituents attached to carbon chain

- named with -yl ending

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Functional Groups

- Determine molecular reactivity and solubility

- Characteristic features

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Alkanes: contain a single C-C bond

Alkenes: contain a double C bond

Alkynes: contain a triple C bond

Properties of Alkanes

- Non-polar

- Insoluble in water

- Less dense than water

- Flammable in air

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double and triple bonds act like a functional group because they can determine reactivity 

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Fewer Hs attached in double and triple bonds

Alcohols

- Alcohol contains a hydroxyl group (OH) attached to a carbon chain

- Phenol contains an OH group attached to a benzene ring

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Ex. C2H6

Alkane: CH3-CH3 (ethane)

Alcohol: CH3-CH2-OH (ethanol)

Naming Alcohols

  1. Name the longest carbon chain containing the --OH group (replace alkane name with ol)​​

  2. Number the longest chain starting at the end closest to the --OH group

  3. Name and number the other substituents relative to the --OH group

  4. Name a cyclic alcohol as cycloalkanol

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Classification of Alcohols 

- Determined by the number of carbon groups (alkyl groups) attached to the carbon bonded to the hydroxyl group

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Thiols

- Sulfur containing compounds

- Functional group is sulfhydral group (SH)

- Structure is similar to alcohol, except there is an SH group rather than OH

- SH groups are important in protein structure 

- The disulfide bond between two cystines is the most important covalent crosslink between two peptide chains

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Properties of Alcohols and Thiols

- Contain polar OH groups

- Form hydrogen bonds with other alcohols (thiols are similar) 

- Have higher boiling points than alkanes of similar mass (higher temperature to break H bonds) 

- More water soluble than alkanes

- Hydrocarbons combust in the presence of O2

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Oxidation and Reduction (REDOX)

Oxidation: Loss of a H or addition of O, increase in C-O bonds

Reduction: Addition of H or loss of O, decrease in C-O bonds

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Aldehydes and Ketones

- Aldehyde contains a carbonyl group (C=O) attached to at least one H atom

- Ketone contains a C=O in between two carbon atoms

- Aldehydes and ketones with the same number of carbon atoms are structural isomers

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CHO

CCOC

- Double bond in the carbonyl group

- Carbonyl has dipole

- The O has 2 lone electron pairs, therefore more EN

- Polarity influences chemical and physical properties

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Oxidation of alcohol into Aldehyde and Ketones

Naming Aldehydes

  • ​An aldehyde has an IUPAC name in which the -e in the alkane name is changed to -al

  • The aldehyde group is always in the 1 position - its at the end

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Naming Ketones

  • The -e in the alkane is replaced with -one

  • The alkyl groups attached to the carbonyl group and named alphabetically followed by ketone

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Properties of Aldehydes and Ketones

- Polar carbonyl groups 

- Attraction between polar groups

- Higher boiling points than alkanes of similar mass

- Lower boiling points than alcohol's of similar mass

- Aldehydes and ketones do not form H bonds with each other, but they do with water

- The longer the carbon chain, the less soluble in water

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Carboxylic Acid

- Carboxylic acids contain the carboxyl group (COOH), which is a carbonyl group attached to a hydroxyl group

- Carboxyl group is found on carbon 1

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Naming Carboxylic Acids

  • Replace the -e in the alkane with -oic acid

  • Number substituents from the carboxyl carbon 1

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Polarity

  • Carboxylic acids have two polar groups (OH and C=O) 

  • Form dimers between two carboxyl groups (therefore have higher BP than alcohols, ketones, and aldehydes of similar mass) 

  • Carboxylic acids form hydrogen bonds with many water molecules

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Esters

Esters are a reaction of carboxylic acids + alcohol (called esterification)

- The carboxylic acid loses its OH and the alcohol loses an H (forms H2O)

- In an ester, the H in the carboxyl group is replaced with an alkyl group

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Naming Esters

  • The name of an ester contains 

    • the alkyl group from the alcohol​

    • the carbon chain from the acid with -ate ending

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Acid Hydrolysis of Esters

  • An ester reacts with water to produce a carboxylic acid and an alcohol

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Base Hydrolysis of Esters

  • Reaction of an ester with a strong base

  • Produces the salt of a carboxylic acid and an alcohol

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Fats are esters

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©2023 by Syracuse University Dr.Margaret Voss

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