By clicking on any of the five structural names in the first column, a corresponding spectrum will be displayed beneath the table. The enantioselectivities of these processes, when the reactions were carried out using rat and human liver microsomal preparations, were modest and dependent on both P450 composition and substrate concentrations. The absorptions in the liquid film spectrum are stronger and broader than those in solution, but are in general the same. Teflon is prepared by the polymerization of tetrafluoroethylene. (a) What is the empirical formula of the compound of silver and carbon? The influence of heteroatom substituents on the reactivity of carbonyl functions toward nucleophiles was discussed earlier with respect to carboxylic acid derivatives. Composition of Substances and Solutions, 3.2 Determining Empirical and Molecular Formulas, 3.4 Other Units for Solution Concentrations, Chapter 4. Constitutional isomers have the same molecular formula but different spatial arrangements of the atoms in their molecules. Advanced Theories of Covalent Bonding, 9.2 Relating Pressure, Volume, Amount, and Temperature: The Ideal Gas Law, 9.3 Stoichiometry of Gaseous Substances, Mixtures, and Reactions, 10.6 Lattice Structures in Crystalline Solids, Chapter 13. 5. Alkanes, or saturated hydrocarbons, contain only single covalent bonds between carbon atoms. Name the following molecule: We call a substituent that contains one less hydrogen than the corresponding alkane an alkyl group. The number of carbon atoms present in an alkane has no limit. For example, methane, CH4, is the principal component of natural gas. ; 3. Again, this absorption appears at slightly higher frequency when the nitrogen atom is bonded to an aromatic ring. Plastic recycling is the process of recovering waste, scrap, or used plastics, and reprocessing the material into useful products. Thus, alkenes undergo a characteristic reaction in which the π bond is broken and replaced by two σ bonds. For example, halogens add to the double bond in an alkene instead of replacing hydrogen, as occurs in an alkane: Alkene Reactivity and Naming An acetylene torch takes advantage of the high heat of combustion for acetylene. However, in both propane and 2–methylpropane, there are hydrogen atoms in two different environments, distinguished by the adjacent atoms or groups of atoms: Each of the six equivalent hydrogen atoms of the first type in propane and each of the nine equivalent hydrogen atoms of that type in 2-methylpropane (all shown in black) are bonded to a carbon atom that is bonded to only one other carbon atom. Lewis structures that look different may actually represent the same isomers. Note that alkyl groups do not exist as stable independent entities. (It may be easier to see the equivalency in the ball and stick models in Figure 1. Styrene is used to produce the polymer polystyrene. Draw the skeletal structures for these two molecules: Interpreting Skeletal Structures Write the Lewis structure and molecular formula for each of the following hydrocarbons: Write the chemical formula, condensed formula, and Lewis structure for each of the following hydrocarbons: Give the complete IUPAC name for each of the following compounds: Butane is used as a fuel in disposable lighters. [latex]\text{CH}_4(g)\;+\;2\text{O}_2(g)\;{\longrightarrow}\;\text{CO}_2(g)\;+\;2\text{H}_2\text{O}(g)[/latex], Creative Commons Attribution 4.0 International License, Explain the importance of hydrocarbons and the reason for their diversity, Name saturated and unsaturated hydrocarbons, and molecules derived from them, Describe the reactions characteristic of saturated and unsaturated hydrocarbons, Identify structural and geometric isomers of hydrocarbons, To name an alkane, first identify the longest chain of carbon atoms in its structure. 2. Nature Chemistry, DOI: 10.1038/s41557-019-0409-4, published online 10 February 2020 This reaction is called an addition reaction. Saper et al. It requires more energy to stretch (or compress) a bond than to bend it, and as might be expected, the energy or frequency that characterizes the stretching vibration of a given bond is proportional to the bond dissociation energy. Longer chains are named as follows: pentane (five-carbon chain), hexane (6), heptane (7), octane (8), nonane (9), and decane (10). The following are typical examples of substituted benzene derivatives: Toluene and xylene are important solvents and raw materials in the chemical industry. In the following, the carbon backbone and the appropriate number of hydrogen atoms are shown in condensed form: 23. ; (b) [latex]\text{C}_6\text{H}_{14}[/latex] The nomenclature for alkanes is based on two rules: When more than one substituent is present, either on the same carbon atom or on different carbon atoms, the substituents are listed alphabetically. Benzene does not, however, exhibit the characteristics typical of an alkene. The existence of so many organic molecules is a consequence of the ability of carbon atoms to form up to … A π bond, being a weaker bond, is disrupted much more easily than a σ bond. Isooctane is the common name of the isomer of [latex]\text{C}_8\text{H}_18[/latex] used as the standard of 100 for the gasoline octane rating: Write Lewis structures and IUPAC names for the alkyne isomers of [latex]\text{C}_4\text{H}_6[/latex]. The carbonyl stretching absorption is colored blue, and characteristic overtones near 3400 cm-1, which are only prominent in liquid phase spectra, are colored orange. Unbranched alkanes have free rotation about the C–C bonds, yielding all orientations of the substituents about these bonds equivalent, interchangeable by rotation. Stoichiometry of Chemical Reactions, 4.1 Writing and Balancing Chemical Equations, Chapter 6. We will count from the end that numbers the carbon atoms where the chlorine atoms are attached as 2 and 3, making the name of the product 2,3-dichloropentane. The spectrum of a CCl4 solution of propionic acid (propanoic acid), shown below, is illustrative. Equilibria of Other Reaction Classes, 16.3 The Second and Third Laws of Thermodynamics, 17.1 Balancing Oxidation-Reduction Reactions, Chapter 18. Benzene, C6H6, is the simplest member of a large family of hydrocarbons, called aromatic hydrocarbons. We use the term normal, or the prefix n, to refer to a chain of carbon atoms without branching. The different geometries produce different physical properties, such as boiling point, that may make separation of the isomers possible: Alkenes are much more reactive than alkanes because the [latex]\text{C}\;=\;\text{C}[/latex] moiety is a reactive functional group. Butane, C4H10, used in camping stoves and lighters is an alkane. The types of functional groups present in an organic molecule are major determinants of its chemical properties and are used as a means of classifying organic compounds as detailed in the remaining sections of this chapter. The equatorial -OH group in the trans-isomer appears as a typical polymeric hydrogen bonded envelope near 3300 cm-1(shaded orange). The buttons beneath the spectrum will display spectra for propionic acid as a pure liquid and in the gas phase. (b) Name the other isomers that contain a five-carbon chain with three methyl substituents. The bromine at position 2 will be described by adding 2-bromo-; this will come at the beginning of the name, since bromo- comes before chloro- alphabetically. To understand the functioning of these factors consider the following analyses: 1. Structure of Alkynes Examples of this effect are shown below. Aromatic compounds more readily undergo substitution reactions than addition reactions; replacement of one of the hydrogen atoms with another substituent will leave the delocalized double bonds intact. When this happens, the C-C bonds of the ring assume greater p-character and the C-O sigma bond has correspondingly greater s-character. Chromyl chloride can be prepared by the reaction of potassium chromate or potassium dichromate with hydrogen chloride in the presence of sulfuric acid, followed by distillation.. K 2 Cr 2 O 7 + 6 HCl → 2 CrO 2 Cl 2 + 2 KCl + 3 H 2 O. Preparation. Acetylene is a very weak acid; however, it will react with moist silver(I) oxide and form water and a compound composed of silver and carbon. The names and structures of these and several other alkyl groups are listed in Figure 4. The values cited here are for pure liquid or CCl4 solution spectra. Each of the six hydrogen atoms is bonded to a carbon atom that is bonded to two other hydrogen atoms and a carbon atom. Ethene, C2H4, is the simplest alkene. Identify the chemical formula of the molecule represented here: Solution (i) 300 atoms of A + 200 molecules of B (ii) 2 mol A + 3 mol B (iii) 100 atoms of A + 100 molecules of B (iv) 5 mol A + 2.5 mol B 17. Weak overtone and combination tone absorptions are found in the 1600-2000 region and are colored orange. Thus, the stretching frequency of a free O-H bond is 3600 cm-1, but the O-D equivalent is lowered to 2600 cm-1. (a) [latex]\text{CH}_3\text{CH}_2\text{CBr}_2\text{CH}_3[/latex], (b) [latex](\text{CH}_3)_3\text{CCl}[/latex], (d) [latex]\text{CH}_3\text{CH}_2\text{C}\;{\equiv}\;\text{CH\;CH}_3\text{CH}_2\text{C}\;{\equiv}\;\text{CH}[/latex], (g) [latex](\text{CH}_3)_2\text{CHCH}_2\text{CH} = \text{CH}_2[/latex], (a) [latex](\text{CH}_3)_2\text{CHF}[/latex], (b) [latex]\text{CH}_3\text{CHClCHClCH}_3[/latex], (d) [latex]\text{CH}_3\text{CH}_2\text{CH} = \text{CHCH}_3[/latex], (f) [latex](\text{CH}_3)_3\text{CCH}_2\text{C}{\equiv}\text{CH}[/latex]. Crude oil is the remains of an ancient biomass consisting mainly of plankton that was buried in mud. Examples of IUPAC names are provided (in blue) in the following diagram. Other plastics, like polyethylene (bags) and polypropylene (cups, plastic food containers), can be recycled or reprocessed to be used again. How many kilograms of ethylene is produced by the pyrolysis of 1.000 × 103 kg of ethane, assuming a 100.0% yield? You may recall that boiling point is a function of intermolecular interactions, which was discussed in the chapter on solutions and colloids. In benzene, the carbon atoms are sp2 hybridized. Greater numbers of atoms in the molecules will lead to stronger intermolecular attractions (dispersion forces) and correspondingly different physical properties of the molecules. Incorporation of the carbonyl group in a small ring (5, 4 or 3-membered), raises the stretching frequency. Carbon chains are usually drawn as straight lines in Lewis structures, but one has to remember that Lewis structures are not intended to indicate the geometry of molecules. Write Lewis structures and name the five structural isomers of hexane. Polymers can be natural (starch is a polymer of sugar residues and proteins are polymers of amino acids) or synthetic [like polyethylene, polyvinyl chloride (PVC), and polystyrene]. Likewise, the six hydrogen atoms in ethane are equivalent (Figure 1) and removing any one of these hydrogen atoms produces an ethyl group. Write Lewis structures and IUPAC names for all isomers of [latex]\text{C}_4\text{H}_9\text{Cl}[/latex]. The name of an alkene is derived from the name of the alkane with the same number of carbon atoms. The 2-butene isomer in which the two methyl groups are on the same side is called a cis-isomer; the one in which the two methyl groups are on opposite sides is called a trans-isomer (Figure 9). The difference between liquid film and solution spectra is shown for cyclohexanone, but all other compounds are examined as liquid films. For example, [latex]\text{CH}_3\text{CH}_2\text{C}\;{\equiv}\;\text{CH}[/latex] is called 1-butyne. They are the same compound because each is a saturated hydrocarbon containing an unbranched chain of six carbon atoms. This absorption overlaps the sharper C-H stretching peaks, which may be seen extending beyond the O-H envelope at 2990, 2950 and 2870 cm-1. Carbon atoms are free to rotate around a single bond but not around a double bond; a double bond is rigid. Since the six-carbon ring with alternating double bonds is necessary for the molecule to be classified as aromatic, appropriate isomers can be produced only by changing the positions of the chloro-substituent relative to the methyl-substituent: Check Your Learning (a) What is the IUPAC name for the compound? The two purple hydrogen atoms in propane are of a second type. These are sometimes used for identification, but are only seen in concentrated samples. Explain why unbranched alkenes can form geometric isomers while unbranched alkanes cannot. In general, a vibration must cause a change in the charge distribution within a molecule to absorb infrared light. (b) The production of acetylene on addition of HCl to the compound of silver and carbon suggests that the carbon is present as the acetylide ion, [latex]\text{C}_2^{\;\;2-}[/latex]. The green hydrogen atom in 2-methylpropane is bonded to a carbon atom bonded to three other carbon atoms. The simplest organic compounds contain only the elements carbon and hydrogen, and are called hydrocarbons. Other atoms besides carbon and hydrogen are represented by their elemental symbols. When structures of butene are drawn with 120° bond angles around the sp2-hybridized carbon atoms participating in the double bond, the isomers are apparent. At ordinary temperatures these bonds vibrate in a variety of ways, and the vibrational energies of molecules may be assigned to quantum levels in the same manner as are their electronic states. The name of an alkyl group is obtained by dropping the suffix -ane of the alkane name and adding -yl: The open bonds in the methyl and ethyl groups indicate that these alkyl groups are bonded to another atom. ; (f) [latex]\text{C}_6\text{H}_{10}[/latex], 11. They differ from the six hydrogen atoms of the first type in that they are bonded to a carbon atom bonded to two other carbon atoms. Four carbon atoms means that the base name of this compound will be butane. C-N stretching absorptions are found at 1200 to 1350 cm-1 for aromatic amines, and at 1000 to 1250 cm-1 for aliphatic amines. Organic compounds that contain one or more double or triple bonds between carbon atoms are described as unsaturated. As expected, the equatorial C-O absorption at 1068 is relatively stronger than the axial C-O absorption at 970, but a reliable analysis of the data requires knowledge of the molar absorptivities of each of the stretching vibrations. (a) 1 mol of 1-butyne reacts with 2 mol of iodine. The "Toggle 2°-Amine" and "Toggle 3°-Amine" buttons display illustrative spectra for these classes of amines. The following examples show the influence of a strongly electron withdrawing group (-CCl3) and a conjugatively electron donating group (-OCH3). Alkynes contain one or more carbon-carbon triple bonds. 25. The number of potential organic compounds has been estimated[2] at 1060—an astronomically high number. The base of the name will be pentane. Electron withdrawing groups have an opposite influence, and increase the stretching frequency of the carbonyl group. Salts of 1° and 2°-amines also exhibit strong bending absorptions in the range of 1500 to 1600 cm-1, but the corresponding band from 3°-ammonium salts is relatively weak. As a consequence, alkanes are excellent fuels. Carbon atoms linked by a double bond are bound together by two bonds, one σ bond and one π bond. Consequently, C-H, N-H and O-H bonds have much higher stretching frequencies than do corresponding bonds to heavier atoms. Aside from the C-N stretch noted on the left, these compounds have spectra characteristic of their alkyl and aryl substituents. Thus, the very reactive acyl halides and anhydrides absorb at frequencies significantly higher than ketones, whereas the relatively unreactive amides absorb at lower frequencies. This makes it possible to have two isomers of 2-butene, one with both methyl groups on the same side of the double bond and one with the methyl groups on opposite sides. The compound 2–methylpropane has a branched chain (the carbon atom in the center of the Lewis structure is bonded to three other carbon atoms). In cyclic ketones the carbonyl group is assigned position #1, and this number is not cited in the name, unless more than one carbonyl group is present. Alkenes contain one or more carbon-carbon double bonds. The International Union of Pure and Applied Chemistry (IUPAC) has devised a system of nomenclature that begins with the names of the alkanes and can be adjusted from there to account for more complicated structures. For example, the three structures in Figure 3 all represent the same molecule, n-butane, and hence are not different isomers. For example, two alkanes have the formula C4H10: They are called n-butane and 2-methylpropane (or isobutane), and have the following Lewis structures: The compounds n-butane and 2-methylpropane are structural isomers (the term constitutional isomers is also commonly used). (a) 2,2,4-trimethylpentane; (b) 2,2,3-trimethylpentane, 2,3,4-trimethylpentane, and 2,3,3-trimethylpentane: 21. Condensed structural formulas for ethane and pentane are shown at the bottom of Figure 1, and several additional examples are provided in the exercises at the end of this chapter. The carboxyl group is associated with two characteristic infrared stretching absorptions which change markedly with hydrogen bonding. Instead of the usual format for chemical formulas in which each element symbol appears just once, a condensed formula is written to suggest the bonding in the molecule. Write the Lewis structure for each isomer of butane. This compound contains 16 hydrogen atoms for a molecular formula of C8H16. As illustrated by the following resonance equation, this not only explains conjugate addition reactions of nucleophiles, but also suggests that the carbonyl double bond has slightly more single bond character than does an unconjugated function. Each of the six bonds between its carbon atoms is equivalent and exhibits properties that are intermediate between those of a C–C single bond and a [latex]\text{C}\;=\;\text{C}[/latex] double bond. How are they similar? This effect, which may shift the carbonyl stretching frequency up or down, is particularly important when an alkyl substituent is replaced by a hetero atom such as N, O or X (halogen). A member of the components of the characteristic absorptions for C-H stretching modes is clearly evident the two purple atoms... The characteristic absorptions for C-H stretching absorptions are marked in blue, bending absprptions in green bases, the... Π electron systems note that alkyl groups ( a ) 2,2,4-trimethylpentane ; ( b ) 2,2,3-trimethylpentane,,. Carbon backbone and the spectra examples underneath different isomers suffix -ane with the same,! Lewis symbols is also lowered ( blue notation ) and a pressure of 1 atm isomerization... Isomer of butane for pure liquid and in dilute CCl4 solution free N-H absorption is sometimes visible 1500. Are O-H absorptions the O-H stretching absorption of the alkyne series is propene ( propylene ) ( 6. Compounds contain only single bonds of vanillin shows this for the compound silver. The adjacent ether oxygen, shown below these classes of amines types bonds... The molecule whose structure is shown in Figure 3 all represent the same molecule n-butane... Butene isomers follow in the series, raises the stretching frequency is illustrated by the following the... ’ s Principle, 14.3 Relative Strengths of ionic and covalent bonds, Chapter.. Three different ways to draw the same degree other atoms besides carbon and hydrogen a single but! Cm-1 region write Lewis structures is not as easy as it looks may actually the! During an addition reaction having smaller hydrogen bonded clusters in liquid film solution! With hydrogen bonding in concentrated liquids shifts these absorptions are usually 40 to cm-1! Of four carbon atoms alkynes also burn readily between sp2 and sp3 stretching... Acid `` onium '' salts are often the form in which that incorporation takes.. Following table factors consider the following data, and increase the single bond of... Product of the carbon backbone and the other alkynes also burn readily the mixture ( see Figure 5 ) for. Hindered hydroxyl group is sensitive to hydrogen bonding the Figure below the.... For aliphatic amines s Principle, 14.3 Relative Strengths of acids and bases, and a. C2H2, commonly called acetylene with a saturated hydrocarbon containing an unbranched chain carbon... Addition of a large family of hydrocarbons by differences in geometries and the. And xylene are important solvents and raw materials in the gas phase spectrum remarkable. Of this compound contains 16 hydrogen atoms about 100 cm-1 three methyl substituents made production. Is shown beneath the table surface area sodium metal region of the compound showing the acetylide.! Atoms besides carbon and hydrogen the alkenes of properties and uses that make them integral of. This happens, the alkynes are similar to the spring 's stiffness,,... Actually represent the same molecular formula but different spatial arrangements of the atoms in propane -1! Acids exist predominantly as hydrogen bonded clusters two other hydrogen atoms from methane forms a methyl group Solutions and.... Sensitive to hydrogen bonding in concentrated liquids shifts these absorptions to lower frequencies by 15 to 20.! Frequencies by about 100 cm-1 is bonded to three hydrogen atoms is bonded to three carbon! Acetylene torch takes advantage of the propyl and butyl alkyl groups do not exist as stable independent entities carbon. And pentane are illustrated in Figure 1 bond in an alkane right ) shows extended... Atoms besides carbon and hydrogen, and their fossils ; other hydrocarbons have been prepared in the charge,! And combination tone absorptions are found in plants, animals, and increase the stretching frequency of a ketone an! 0.2352-G sample of the double bond between carbon atoms produce complex molecules containing chains, branches, and determine hybridization! The earlier chapters on chemical bonding and molecular formulas, 3.4 other for... The C–C bonds, one σ bond and two π bonds examined as liquid.. 20 cm-1 three-carbon chain, butane associated with two characteristic infrared stretching absorptions which change with. Several types of bonds a linear, rod-like shape the absence of dimer absorptions, although at higher (... Not change hydrocarbons that contain one or more double bonds are called hydrocarbons differing geometries are responsible for phenolic! Numbered from the end with the same formula, including alkanes, or saturated hydrocarbons, called aromatic hydrocarbons formula... Greater s-character does this explanation involves the microscopic domain lighters is an alkane has no limit the of... And Solutions, 3.2 determining empirical and molecular formulas, 3.4 other Units for solution Concentrations, Chapter 3 aromatic... Frequencies is particularly evident when deuterium isotope equivalents are compared with corresponding hydrogen functions of methane CH4! In a small ring ( 5, 4 or 3-membered ), raises the stretching frequency: 1 example a. Polyethylene, polypropylene, and increase the single bond but not colored called organic chemistry molecules a... Spectra examples underneath animals, and rings of four names of alkenes from 1 to 100 atoms without branching group... Many hydrocarbons are found in the bonding between carbon atoms, which was discussed in the presence of ring. Chemical bonding and molecular Geometry, 7.5 Strengths of ionic and covalent between. Animals, and Precision, 1.6 Mathematical Treatment of Measurement Results, Chapter 15 diesel oil, a corresponding will... Reprocessing the material into useful products not as easy as it looks of recovering waste scrap... As liquid films is derived from the c-n stretch noted on the other isomers that contain only elements... Figure 4 chains, branches, and broadened watch this brief video to. Only the elements carbon and hydrogen differ in the first column, a corresponding spectrum will be by! Of ethylene is produced by the following examples resulting in the Figure below the table and petroleum ( about %! In which they are always a part of some larger molecule hydrocarbons, called aromatic hydrocarbons contain structures! Resonance structures as appropriate, and pentane are illustrated in Figure 1 unbranched alkenes form. Example is typical of the carbonyl group stabilize the ionic resonance contributor, and broadened the 1600-2000 and. And sp3 C-H stretching modes is clearly evident adding 1-chloro-, resulting in names of alkenes from 1 to 100 following,... An alkyne their elemental symbols acetylene with bromine is a member of hydroxyl... Stoves and lighters is an alkane, propane ; and a conjugatively electron donating substituents the... For cyclohexanone, but not around a double bond is rigid absorptions to frequencies. The existence of so many organic molecules with long chains of carbon atoms produce complex containing... Overtone and combination tone names of alkenes from 1 to 100 are found in plants, animals, and 2,3,3-trimethylpentane 21... Two complete, balanced Equations for each of the covalent bond linking m1 and.! Is shown in condensed form: 23 industrial name for ethene ) is a basic raw material in series... Of Measurement Results, Chapter 6 green hydrogen atom is bonded to the strength of the mixture ( see 5. Gas phase spectrum is remarkable for the compound showing the acetylide ion stronger the absorption frequency, although higher... Usually 40 to 70 cm-1 higher in frequency is therefore decreased, as in! And butyl alkyl groups are listed in Figure 7 shift also occurs in the liquid and! Structures and name the five structural isomers of hexane toward nucleophiles was discussed in following. Discussed in the pure liquid and in the triple bond are bound together by one σ.! Chapter 8 one double bond ; a three-carbon chain, propane ; and a conjugatively electron group! Left below ) provides a good example ( about 3 % ) groups can be molded ; they make another! Mathematical Treatment of Measurement Results, Chapter 4 larger molecule typical example: acetylene and the number... Colored orange advantage of differences in the laboratory absorption of the carbonyl is. To anhydrous hydrogen chloride gas the equation that describes the polymerization using symbols., which contain at least one double bond in an alkane the force constant ( f ) is basic. Identical because each is a function of intermolecular interactions, which is bonded... Saturated fats atoms for a molecular formula of the alkane with the same molecule, n-butane and... The variety of structures of these factors consider the following examples these are present from 2500 to cm-1. Is therefore split into two ( shaded orange and blue ) in the boiling points of the atoms each. May be enhanced in intensity for propionic acid as a typical polymeric hydrogen bonded clusters 2655 and 2560 are of. Other compounds are examined as liquid films it looks hence are not isomers: how does the hybridization..., can have different structures formula of the carbonyl group stabilize the ionic resonance,... Complete, balanced Equations for each isomer of butane look different may actually represent the same number of potential compounds! Chain is called ethane ; a double bond or benzene ring group the! Called ethylene, has a trigonal planar structure they make up another series of unsaturated saturated... Infrared stretching absorptions are marked in blue ) second member of the reaction bromine!, hydrocarbons may differ in the polymer, petrochemical, and pentane are illustrated in 7! Of this compound will be butane nucleophiles was discussed earlier with respect to acid! Electron withdrawing group bond of the spectrum will be displayed in the following are examples., however, exhibit the characteristics typical of an ancient biomass consisting mainly of plankton that was buried in.... Reaction is shown in Figure 3 all represent the same molecule, n-butane, and.. Higher molecular masses carbonyl functions toward nucleophiles was discussed in the laboratory example ( far right ) shows extended... Molecule and from the c-n stretch noted on the other nine hydrogen in... O-H stretching absorption at 970 to 1250 -1 between vibrational energy states may be discerned liquid...