part 1 organic materials Flashcards
What were the first artificial pigments? How is it a marker of technology in human evolution?
Carbon black (charcoal) was the first artificial pigment, created by ‘burning’ in limited air, wood, bark, bones or ivory. The first black pigments could be composed of manganese oxide, a naturally occuring mineral, or charcoal, present in nature but created by man for specific uses.
Charred biomass provides indication of fire. The presence of flint and human activities may indicate the fire was not natural (lightning-sparked wildfire), but ignited by humans.
What is the different between graphite, coal, charcoal, char?
- Chemical composition: graphite is composed of 100% of carbon, when charcoal does not consist exclusively of carbon. Other elements are present, for instance oxygen and hydrogen. The chemical composition is variable.
- atom connectivity: same elemental composition but different disposition in space, giving different properties
DEF qualitative analysis
Analysis in which substances are identified or classified on the basis of their chemical or physical properties, such as chemical reactivity, solubility, molecular wieght, melting point, radiative properties (emission, absorption), mass spectra, nuclear half-life
DEF quantitative analysis
Analysis in which the amount or concentration of an analyte may be determined (estimated) and expressed as a numerical value in appropriate units.
/!\ qualitative analysis may take place without quantitative analysis but quantitative analysis requires the identification (qualification) of the analytes for which numerical estimates are given.
Different types of formula to represent a molecule’s composition
Empirical formula: The simplest formula expressing the composition. It can be expressed on the weight basis or on the molar (atomic) basis.
Next two are also representing the connectivity/bonding:
- Molecular formula: empirical formula in accordance with the atomic composition of the molecule
- structural formula: the way atoms are connecnted and located in space
(line formula: A two-dimensional representation of molecular entities in which atoms are shown joined by lines representing single or multiple bonds. Without any indication or implication concerning the spatial direction of bonds.)
DEF chemical compound & organic compound
Chemical compounds are any substance composed of identifcal molecules consisting of atoms of two or more chemical elements
Organic compounds are all the compounds containing carbon excluding carbonayes, cyanides, and a few others.
Oxalic acid formulas
Empirical formula: HCO2
Molecular formula: H2C2O4
Some chemical class and their functional group
- carboxylic acids: R-COOH)
- hydrocarbons: composed only of carbons and hydrogen
- alcohols: functional group hydroxy (R-OH with R an alkyl or aryl radical)
- aldehydes, ketones: functional group is carbonyl R2C=O, R(H)C=O
DEF isomers
Different compounds that have the same atomic composition (molecular formula) but different line formulae or different stereochemical formulae and hence different physical and/or chemical properties.
DEF stereoisomers
Isomerism due to differences in the spatial arrangement of atoms without any differences in connectivity or bond multiplicity between the isomers.
DEF enantiomers
Stereoisomers which are mirror images of each other and nonsuperimposable (possible nomenclature of the two forms: (+)/(-), R/D, L/D, R/S…)
DEF diastereoisomers
Stereoisomers that are not mirror images of each other
Molecular marker of wine
L(+)-tartaric acid
Molecular marker of fermentation processes to produce food and fermented beverages
Lactic acid
Molecular marker of beer
Calcium oxalate
Name the two origins of indigo. How to recognize the natural from synthetic indigo?
- Naturally from the extraction of plant leaves, then hydrolysis and oxidation to obtain indoxyl (precursor of indigo)
- Another pathway: from the coal tar produced in the steel industry as a byproduct, then extraction. Isatin obtained, precursor of indigo.
Natural indigo can be differenciated from synthetic indigo by
- analysis of by-products
- 13C/12C ratio
What are organic materials made of?
Organic materials can be composed of individual structurally defined organic compounds (monomers, dyes, enzymes, characterised for instance by a specific molecular mass), polymers with defined molecular structure but composed of chains with different molecular mass (cellulose) or heterogeneous complex molecular structures not representable by specific molecular formulae (coal, resins).
Classification of organic materials
It can be based on a molecular basis or on the type of application
- lipids: soluble in non-polar solvents (sterols, acilglycerols, waxes, terpens, binders, fuels)
- glucids: polyhydroxy ketones aldehydes (papers, textile, adhesives)
- protids: polyamides (clothes & glue)
- others: pigments, protectives…
The analytical methods are based on the chemical nature of the analyte.
Important properties for chemical analysis
- The molecular mass is expressed in terms of relative unit mass. In many cases, organic materials in CH have complex structures. A MW cannot be established. (carbon black has an “infinite” MW)
- Volatility is a way to express the tendency of a substance to go into the gas phase. It is determined by measurable properties:
- vapour pressure: pressure of the pure substance in equilibrium with its liquid phase
- boiling point: temperature at which vapour pressure equals atmospheric pressure
The vapor pressure is increasing with decreasing boiling point. For compounds belonging to the same chemical family, volatility decreases with increasing molecular mass.
Cohesive forces keep the molecules bonded together –> increase with increasing molecular weight –> if stronger cohesive forces, less molecules have enough energy to go in the gas phase
For compounds not belonging to the same chemical family, volatility also depends on polarity.
- The polarity is a molecular characteristic due to the non-symmetric electric charge distribution when bonded atoms have different electronegativity. A polar molecule has a permanent dipole moment. Polarity can be extended to molecules that do not exhibit a permanent dipole moment. Instantaneous dipole moments are formed due to molecular motion and intermolecular interactions.
- Polarizability is the molecular characteristic that express the tendency of a molecule to form induced dipoles. A molecule with “mobile” electrons, like pi electrons, has a large polarizability.
As polarizability increases, the atomic mass increases, the intermolecular interactions increase
Polarizability and polarity determine the entity of intermolecular interactions e.g cohesive forces in the liquid and in turn volatility and water solubility.
- Hydrogen bonds is a particular and important type of dipolar interaction that
occurs when hydrogen atom is bound to a highly electronegative element, such as N
and O.
DEF amphiphatic compounds
Contains both a hydrophilic and a hydrophobic (lipophilic) group.
